INTRODUCTION
Kummell disease (KD), also known as vertebral ischemic osteonecrosis, is manifested by vertebral osteonecrosis and accompanied by vertebral instability, progressive kyphosis, and even neurological dysfunction. Almost all patients with KD have osteoporosis, so KD is also called symptomatic choracic osteoporotic vertebral fracture [1-3]. It usually involves a single vertebra, and is mostly observed in the thoracolumbar segment [2]. Intravertebral vacuum cleft (IVC), as the signature pathological feature of KD, plays a pivotal role in the diagnosis of KD [4]. The sensitivity and specificity of IVC in the diagnosis of KD is 85% and 99% respectively, meaning that KD is usually accompanied by IVC [5-7].
KD is extremely rare in patients without osteoporosis, and it is often secondary to osteoporotic fractures. With today’s aging population and the increasing number of patients with osteoporotic vertebral fracture, the number of KD patients is also increasing [8,9]. Conservative treatment does not have a satisfactory efficacy and may further deteriorate the symptoms, so it has gradually become an adjunctive therapy for the surgical treatment [1,10,11]. With the progress in minimally invasive technology for the spine, percutaneous vertebroplasty (PVP) has become the mainstream therapy for unstable KD for its outstanding pain relief effect and improvement of kyphosis [2,12,13]. Recovery of spinal stability and complete IVC filling by bone cement are the most important analgesic mechanisms in KD. However, due to the inability of bone cement in IVC to infiltrate normal bone tissues, the postoperative loosening rate of cement can reach as high as 25%, leading to recurrent and even more severe pain for patients [14]. Meanwhile, bone cement loosening may further lead to the disastrous complication of cement displacement, causing the patients to take out bone cement and undergo open surgery to rebuild spinal stability. Both anterior and posterior revision surgeries have the disadvantages of large trauma, high difficulty and high risk.
Any therapy that can avoid severe complications should be the best treatment. In past clinical work, our center used the percutaneous pediculoplasty (PPP) combined technique during PVP (PVP-PPP) and PVP-bone cement bridging screw system (Changzhou Geasure Medical Apparatus and Instruments Co., Ltd., Changzhou, China) combined technique to avoid bone cement loosening and displacement in unstable KD patients. Our previous studies involving 3-dimensional finite element analysis and biomechanical investigations have unequivocally demonstrated the substantial superiority of these 2 treatment methods over PVP [15,16]. These 2 therapies intend to link the bone cement in IVC to normal bone tissues in the vertebrae as a “bridge” to anti bone cement loosening or displacement. It is the first time for both techniques to be used to avoid postoperative cement loosening or displacement in KD, and there were several problems need to be solved: (1) What are the differences in actual clinical efficacy, such as complication, pain relief and functional improvement, between these 2 therapies? (2) Can the bone cement bridging screw system effectively avoid bone cement loosening and displacement? (3) What are the difficulties, advantages and disadvantages of these 2 therapies? Given these, we carried out this retrospective case-control study on 119 patients who were treated with these 2 therapies and were followed up on for over 2 years during a 4-year period to define the above scientific questions.
MATERIALS AND METHODS
1. Patients
This clinical study protocol was approved by the Institutional Review Board of Honghui Hospital of Xi’an Jiaotong University (approval number: 201701007). All patients signed the written informed consent.
One hundred nineteen patients with single-segment KD in the thoracolumbar segment and without neurological symptoms were included in this study from January 2017 to May 2021. All patients met the criteria for diagnosis of unstable KD. The changes in the angles between the extension line of the upper endplate and the extension line of the lower endplate of the affected vertebra in the forward flexion position (vertebral body angle) and in the posterior extension position were compared in the thoracolumbar dynamic position x-ray films. When the change was > 11°, the patient was defined to have dynamic instability of the affected vertebra and was diagnosed with unstable KD [17]. All patients had the main symptom of severe pain in the corresponding affected part or lower waist when the body position changed due to instability, and had it progressively aggravated.
Inclusion criteria: (1) patients with single-segment unstable KD; (2) patients whose bone mineral density (BMD) T-value was below -2.5; (3) patients with severe lumbago and backache but without neurological impairment; (4) patients having bilateral pedicles intact and not damaged.
Exclusion criteria: (1) patients with neurological symptoms; (2) patients with multivertebral lesions; (3) patients also with a metastatic spinal tumor, lumbar spondylolisthesis, and other diseases that caused lumbago and backache; (4) patients without osteoporosis; (5) patients with congenital absence, deformity or damage of the pedicle of the affected vertebra; (6) patients who were followed up on for less than 2 years.
All patients underwent plain radiography, dynamic position x-ray, computed tomography (CT) and magnetic resonance imaging examinations. The x-ray films and CT findings before and after operation were retrospectively compared and analyzed. By surgical method, the patients were divided into 2 groups. Those who received the PVP-PPP combined therapy were grouped to the PPP group, and those who received the PVP-bone cement bridge screw system combined therapy were grouped to the screw group.
2. Surgical Methods
1) PVP-PPP combined therapy
After general anesthesia, a patient was placed in the prone position, and had soft pads under the chest and anterior superior iliac spine to completely suspend the abdomen. Under the lateral C-arm fluoroscopy, the operating bed was adjusted so that the patient was in an appropriate hyperextension position. Manual compression reduction was used for optimal vertebral height recovery. After satisfactory reduction, C-arm fluoroscopy was used to mark the body surface projection of the lateral margin of bilateral pedicle of the affected vertebra. After disinfection and draping, a unilateral puncture operation was performed on the side with a larger IVC fissure on the CT cross section. According to the distance from the body surface of the patient’s affected site to the articular process, the skin was incised longitudinally 5 to 10 mm outside the body surface marker, with the incision of about 5 mm in length. A 3.0 mm-diameter bone cement trocar was used for puncture. Along the direction of the pedicle of the affected vertebra, the bone cement trocar was ensured to target and puncture into IVC inside the pedicle. C-arm fluoroscopy was used several times to verify the accuracy of the position of the bone cement trocar. With a satisfactory position of the trocar as verified, bone cement was prepared and, when it was in the wire-drawing stage, an appropriate volume was slowly injected under anteroposterior-lateral xray fluoroscopy, till the interspaces in the affected vertebra were fully filled. PVP was thus done. After that, when the bone cement was in the toothpaste-like stage, the slow injection of it was continued under lateral x-ray fluoroscopy, while the trocar was slowly receded toward the backside. These 2 operations should be performed in perfect union. Bone cement injection ended when the trocar was receded throughout the entire pedicle and close to the initial puncture point. PPP was thus done. After bone cement had completely set, the trocar was withdrawn. The detailed diagrams illustrating the surgical technique are presented in (Fig. 1C–E), while (Fig. 2B and D) display postoperative x-ray and CT data of a representative patient.
2) PVP-bone cement bridge screw system combined therapy
After general anesthesia, a patient was placed in the prone position. Similarly, after satisfactory reduction, C-arm fluoroscopy was used to mark the body surface projection of the lateral margin of bilateral pedicle of the affected vertebra. Through a unilateral approach, the operation was performed on the side with more severe vertebral fissures on the CT cross section. Depending on the patient’s body shape (fat or thin), the skin was incised longitudinally 5 to 10 mm outside the body surface marker, with the incision of about 10 mm in length, and then subcutaneous tissues and lumbodorsal fascia were incised layer by layer. Under the guidance of anterior-posterior x-ray fluoroscopy, the puncture needle tip was placed at the outer margin of the projection of the pedicle (The left corresponds to the 10 o’clock position, while the right corresponds to the 2 o’clock position), and then the puncture was performed at the fracture in the vertebral body of the affected vertebra with an inward tilt of 10° to 15°. Under, When the puncture needle tip reached the posterior edge of the vertebral body under the guidance of lateral x-ray fluoroscopy, the anterior-posterior x-ray fluoroscopy was used again, under which the puncture needle tip did not break through the medial margin in the projection of the pedicle (this step could avoid the screw going into the spinal canal as much as possible). After that, the targeted puncture was continued into the fissure in the vertebral body under lateral x-ray fluoroscopy, and the guide needle was placed in. Under the guidance of the guide needle, a new-type bone cement bridge screw with a bone cement outlet was placed into IVC inside the vertebral body of the affected vertebra. The screw placing handle and the core of the screw placing extension rod were then removed. Bone cement was prepared, and injected into a special push rod for the bone cement bridge screw. When bone cement was in the wire-drawing stage or clustering stage, an appropriate volume of bone cement was slowly injected along the core of the extension rod under anteroposterial-lateral x-ray fluoroscopy. After IVC in the vertebral body of the affected vertebra was fully filled, bone cement injection ended. After bone cement had completely set, the screw tail extension rod was removed and the incision was sewn up. The detailed diagrams illustrating the surgical technique are presented in (Fig. 1F–H), while (Fig. 2A and C) display postoperative x-ray and CT data of a representative patient.
3. Postoperative Treatment
After the patient woke up from general anesthesia, he/she was observed for symptoms of nerve damage. After the operation, patients were routinely given antibiotics for 24 hours, and asked to rest in bed until 1 day after operation, when they could get out of bed and move under the protection of braces. The rehabilitation doctors guided postoperative functional exercises and matters needing attention. The patients were discharged after having stable disease development. After discharge, the patients were asked to keep wearing the braces for protection for 12 weeks, and also to take calcium supplements, Vitamin D3 and diphosphonates to treat osteoporosis under the guidance of osteoporosis doctors.
4. Follow-up Evaluation
Follow-up evaluations were carried out at 6 months, 1 year, and 2 years after operation. X-ray or CT was used to evaluate whether bone cement was displaced and whether the bone cement bridge screw was loose, displaced or broken. The vertebral body index (VBI), which represents the ratio of anterior to posterior vertebral height multiplied by 100% for the affected vertebral body, was measured to assess postoperative improvement in vertebral body height. The bisegmental Cobb angle, defined as the angle between the upper endplate of the first vertebra above the affected one and the lower endplate of the first vertebra below it, was measured to evaluate kyphosis correction (Fig. 3). CT was used to evaluate bone cement loosening. The criterion for bone cement loosening was defined as the presence of a continuous low-density region observed between the bone tissues and bone cement during CT follow-up examinations [14].
The comparison results of the patients’ visual analogue scale (VAS) were used to evaluate pain relief in the patients, with the score ranging from 0 to 10 points.
The comparison results of the patients’ Oswestry Disability Index (ODI) scores were used to evaluate the recovery of thoracolumbar functions in the patients. The ODI questionnaire has 10 questions covering the intensity of pain, personal care, lifting, walking, sitting, standing, sleeping, sex life, social life and traveling. Each question has 6 options, and is scored 0 to 5 points. ODI is used to evaluate the degree of impact of low back and leg pain on the daily life of patients. The calculation formula is ODI (%)= actual score/(actual number of questions answered × 5)× 100%.
5. Statistical Analysis
This study is a retrospective cohort study. It used the IBM SPSS Statistics ver. 26.0 (IBM Co., Armonk, NY, USA) statistical software package for statistical analysis. All measurement data were expressed as (mean ± standard deviation). The results of VBI, bisegmental Cobb angle, VAS, and ODI of the same group before operation, after operation and at the last follow-up visit were compared using repeated measures analysis of variance. Pairwise comparisons of VBI, bisegmental Cobb angle, VAS, or ODI were conducted using paired t-test. Results of them of the PPP group and the screw group were compared using independent samples t-test. Postoperative bone cement loosening of the 2 groups was compared using Fisher exact test. Enumeration data of the 2 groups were compared using chi-square test. When p < 0.05, the difference was deemed significant.
RESULTS
1. Operation Results
Among the 119 patients, 77, including 19 males and 58 females, were grouped to the PPP group. They were 72.52 ± 5.44 years old on average (range, 63–85 years), their preoperative BMD T-value measured by dual x-ray absorptiometry was -3.21 ± 0.57 on average (range, -2.5 to -5.2), and 3 had segment T10 affected, 9 had segment T11 affected, 37 had segment T12 affected, 21 had segment L1 affected, and 7 had segment L2 affected. The screw group had 42 patients, including 11 males and 31 females. They were 74.36 ± 5.07 years old on average (range, 64– 88 years), their preoperative BMD T-value measured by dual x-ray absorptiometry was -3.38 ± 0.51 on average (range, -2.6 to -4.5), and 2 had segment T10 affected, 5 had segment T11 affected, 19 had segment T12 affected, 13 had segment L1 affected, and 3 had segment L2 affected. Statistical analysis showed that there were no significant differences in age, sex, BMD and affected segment between the 2 groups (p > 0.05), and the baseline data of the 2 groups were comparable. All 119 patients had the operation successfully done. The average operation duration of the PPP group was 85.52 ± 10.78 minutes (range, 70–115 minutes), and its average bone cement injection volume was 4.98 ± 0.67 mL (range, 4–6 mL). The average operation duration of the screw group was 52.07 ± 9.90 minutes (range, 36–65 minutes), and its average bone cement injection volume was 4.43 ± 0.89 mL (range, 2.5–6 mL). The screw group had a shorter operation duration and less bone cement volume than the PPP group, indicating that the PVP-bone cement bridge screw system combined therapy could shorten the operation duration and reduce bone cement volume. Among the 119 patients, 111 were not observed bone cement leakage (93.28%) and 8 had bone cement leakage (6.72%). In the PPP group, 6 patients had bone cement leakage, including 2 had it leak from the anterior margin of the vertebral body, 2 had it leak from the paravertebral vein, 1 had it leak from the sidewall of the vertebral body and 1 had it leak from the superior intervertebral disc. In the screw group, 2 had bone cement leakage, including 1 had it leak from the anterior margin of the vertebral body and 1 had it leak from the sidewall of the vertebral body. None of the patients had leakage inside the spinal canal or from the intervertebral foramen. None of the 119 patients had severe complications, such as symptoms of nerve root irritation and damage of large blood vessels or spinal marrow, after they got out of bed and moved. All patients had sound incision healing, and none of them had delayed incision healing, infection or hematoma formation. Ninty-two patients were discharged on 2 days after operation, and the remaining 27 were discharged from 3 days to 5 days after operation. The basic information and clinical information of the patients were demonstrated in (Table 1).
2. Follow-up Visit Results
During the 2-year follow-up, no patient in the screw group had screw loosening, displacement or fracture, no had bone cement loosening or delayed displacement, and no received revision surgery. Besides, during the follow-up, no patient had skin or soft tissue wear or discomfort caused by the screw. In the PPP group, 11 patients had bone cement loosening (14.29%), and no had bone cement displacement or received revision surgery. Analysis of the bone cement loosening of the 2 study groups by Fisher exact test showed that the PPP group had 11 patients with bone cement loosening, significantly greater than 0 patients in the screw group, with the difference of significant statistical significance (p = 0.008) (Table 1).
The evaluation of the improvement of the vertebral body height of the affected vertebra showed that the VBI of the PPP group improved from 62.51 ± 6.88 before operation to 83.28 ± 2.15 after operation, with the difference of statistical significance (p < 0.001), and although VBI dropped slightly in later follow-up visits and to 82.60 ± 2.18 at the last follow-up visit, the differences between it and that immediately after operation and at 1 year after operation (82.69 ± 2.22) were not statistically significant (p = 0.056, p = 0.790). The evaluation also showed that the VBI of the screw group improved from 62.02 ± 6.89 before operation to 83.70 ± 2.32 after operation, with the difference of statistical significance (p < 0.001), and although VBI dropped slightly in later follow-up visits and to 83.53 ± 2.45 at the last follow-up visit, the differences between it and that immediately after operation and at 1 year after operation (83.55 ± 2.19) were not statistically significant (p = 0.752, p = 0.967). The statistical results of VBI of the 2 groups were demonstrated in (Table 2, Fig. 4). The comparison of VBI scores between the 2 groups at different follow-up time points showed that the VBI score improved more significantly after the PVP-bone cement bridge screw system combined therapy. There was no significant difference in VBI score between the PPP group and the screw group before and immediately after operation and at 6 months after operation (p > 0.05), but the follow-up visits at 1 year and 2 years after operation showed that there were significant statistical differences between the screw group (83.55 ± 2.19 at 1 year after operation, 83.53 ± 2.45 at 2 years after operation) and the PPP group (82.69 ± 2.22 at 1 year after operation, 82.60 ± 2.18 at 2 years after operation) (p < 0.05).
The evaluation of kyphosis correction showed that the bisegmental Cobb angle of the PPP group was corrected from 29.06° ± 3.89° before operation to 16.01° ± 3.53° after operation, with the difference of statistical significance (p < 0.001), and at the last follow-up visit, the patients had the thoracolumbar kyphosis angle slightly increase, to 17.06° ± 3.70° on average, but the differences between it and that immediately after operation and at 1 year after operation (16.81° ± 3.61°) were not statistically significant (p = 0.057, p = 0.697). The evaluation also showed that the bisegmental Cobb angle of the PPP group was corrected from 29.19° ± 4.12° before operation to 14.72° ± 3.52° after operation, with the difference of statistical significance (p < 0.001), and at the last follow-up visit, the patients had the thoracolumbar kyphosis angle slightly increase, to 15.56° ± 3.25° on average, but the differences between it and that immediately after operation and at 1 year after operation (15.40° ± 3.66°) were not statistically significant (p = 0.270, p = 0.858). The statistical results of the bisegmental Cobb angle of the 2 groups were demonstrated in (Table 3, Fig. 5). The comparison of the bisegmental Cobb angle between the 2 groups at different follow-up time points showed that the bisegmental Cobb angle after the PVP-bone cement bridge screw system combined therapy was significantly smaller than that of the PPP group. There was no significant difference in bisegmental Cobb angle between the PPP group and the screw group before and immediately after operation and at 6 months after operation (p > 0.05), but the follow-up visits at 1 year and 2 years after operation showed that there were significant statistical differences between the screw group (15.40° ± 3.66° at 1 year after operation, 15.56° ± 3.25° at 2 years after operation) and the PPP group (16.81° ± 3.61° at 1 year after operation, 17.06° ± 3.70° at 2 years after operation) (p < 0.05).
The VAS pain score and ODI function score of the PPP group improved from 7.47 ± 0.35 and 78.08 ± 4.49 points before operation to 2.91 ± 0.30 and 50.39 ± 5.75 points after operation, 2.14 ± 0.35 and 21.21 ± 2.83 points at 1 year after operation, and 2.09 ± 0.33 and 20.47 ± 2.90 points at the last follow-up visit. The VAS score improved by 72.02% and the ODI score improved by 73.78% from that before operation to that at the 2-year last follow-up visit. When comparing either of the 2 scores before operation, that after operation, that at 6-month follow-up visit and that at the last follow-up visit, there were statistically significant differences (p < 0.05), while there were no statistically significant differences between either of them at 1 year after operation and that at the last follow-up visit (p = 0.337, p = 0.083). The VAS pain score and ODI function score of the screw group improved from 7.55 ± 0.27 and 76.90 ± 4.77 points before operation to 2.81 ± 0.41 and 49.19 ± 3.87 points after operation, 2.00 ± 0.40 and 20.33 ± 2.64 points at 1 year after operation, and 1.87 ± 0.30 and 19.32 ± 2.60 points at the last follow-up visit. The VAS score improved by 75.23% and the ODI score improved by 74.88 from that before operation to that at the 2-year last follow-up visit. When comparing either of the 2 scores before operation, that after operation, that at 6-month follow-up visit and that at the last follow-up visit, there were statistically significant differences (p < 0.05), while there were no statistically significant differences between either of them at 1 year after operation and that at the last follow-up visit (p = 0.091, p = 0.060). The statistical results of the VAS and ODI scores of the 2 groups were demonstrated in (Tables 4, 5; Figs. 6, 7). The comparison of the VAS pain score and ODI function score between the 2 groups at different follow-up time points showed that the VAS and ODI scores after the PVP-bone cement bridge screw system combined therapy were significantly smaller than those of the PPP group. There was no significant difference in VAS or ODI score between the PPP group and the screw group before and immediately after operation and at 6 months and 1 year after operation (p > 0.05), but at the 2-year follow-up visit, there were significant statistical differences between the screw group (1.87 ± 0.30, 19.32 ± 2.60) and the PPP group (2.09 ± 0.33, 20.47 ± 2.90) (p < 0.05).
DISCUSSION
As the global population aging aggravates, the number of patients with osteoporotic fracture of the vertebral body is increasing year by year, and so is the incidence rate of KD [1,9,18,19]. IVC is the characteristic imaging manifestation of KD, and it, as the characteristic pathological change, causes the loss of spinal stability in KD and neuropathic pain in patients [4,20].
Different surgical methods, such as PVP, percutaneous kyphoplasty (PKP), percutaneous fixation, open reduction and osteotomy-orthopedics have been reported in literature [21-28]. Although PVP can satisfactorily relieve pain and improve kyphosis and has become one of the most important ways to treat KD, the surgical therapies for KD are still controversial in clinical practice. IVC is a dead cavity formed by pathologically confirmed necrotic bone tissues. Filling it with bone cement can rebuild spinal stability and relieve patients’ pain. However, it is difficult for bone cement to penetrate into the normal trabecular structure, and bone cement occupies fissures only and has no mechanical interlocking or biocompatibility with the surrounding bone tissues, so the two are not bonded. Therefore, even if the postoperative efficacy is satisfactory, there are still risks of bone cement loosening and displacement during follow-up visit.
In this study, we used the PVP-bone cement bridge screw system combined therapy for KD to investigate the differences in efficacy between it and the PVP-PPP combined therapy, as well as its clinical effectiveness. With the use of the bone cement bridge screw system, bone cement in IVC can join the whole vertebral body through the bone cement bridge screw and the bone cement inside the screw, thus avoiding the risks of bone cement loosening and displacement. None of the 42 patients in the screw group had postoperatively delayed bone cement loosening or displacement, while 11 of the 77 patients in the PPP group had it (p = 0.008), which well demonstrated the effectiveness of the fixation strength of the bone cement bridge screw system. After 2 years of follow-up evaluations, all patients had imaging parameters significantly improved. The statistical analysis results showed that, although there was no significant difference in the improvement of VBI or bisegmental Cobb angle between the screw group and the PPP group immediately after operation and at 6 months after operation (p > 0.05). the screw group had significantly higher VBI and bisegmental Cobb angle than the PPP group at 1-year and 2-year midterm postoperative evaluations (p < 0.05). Moreover, in terms of pain relief and functional improvement, there was no significant difference in VAS pain score or ODI function score between the screw group and the PPP group before and immediately after operation and at 6 months and even 1 year after operation (p > 0.05). However, at 2 years after operation, the screw group had higher VAS pain and ODI function scores than the PPP group (p < 0.05). Bone cement loosening is closely related to the patient’s imaging manifestations and pain degree. Bone cement loosening causes the anterior margin of the patient’s vertebral body to collapse slightly, the correction of the patient’s VBI and bisegmental Cobb angle to loosen, the patient’s pain to deteriorate, and the patient’s functions to be affected. The results of this study proved that the PVP-bone cement bridge screw system combined therapy was safer and more effective for unstable KD than the PVP-PPP combined therapy. After PVP-PPP treatment, it is evident from the outcomes that bone cement loosening results in heightened pain levels and diminished lumbar function among patients, frequently observed 1 year after surgery.
The cause of bone cement loosening and displacement after KD surgery is still unknown. We summarized and analyzed the information of almost all KD patients with bone cement displacement after PVP or PKP reported in literature in recent years [29-35], and found that all these patients had bone defects at the anterior margin of the vertebral body and bone cement relocated from the anterior part of the defected vertebral body to the ventral part. Although dynamic x-ray images have not been used to measure changes in vertebral body angle, the majority of cases can be inferred as unstable KD based on the alterations in preoperative and postoperative vertebral body angles and significant anterior vertebral bone defects. During PVP, bone cement tends to be distributed at the anterior margin of the vertebral body under the action of injection pressure, and it easily penetrates into the anterior vertebra in the event of insufficient bone mass at the anterior margin of the vertebral body. Even if the correction of kyphosis is significantly improved after operation, the patient may still have mild kyphosis after operation, so in postoperative movements, the center of gravity of the affected vertebra moves forward and the stress extrudes bone cement to produce a forward force, thus causing bone cement to move forward if the anterior margin of the vertebral body lacks the bone battier. Furthermore, in unstable KD, after the filling by bone cement, some patients may still have poor stability in the affected vertebra and are likely to have bone cement loosening or even displacement under repeated flexion and extension activities after operation. Due to the presence of IVC, it is difficult for bone cement to penetrate into the normal trabecular structure, and bone cement occupies fissures only and has no mechanical interlocking or biocompatibility with the surrounding bone tissues, which is another important reason for bone cement leakage, loosening and displacement [36].
Given the above factors, we developed a new-type bone cement bridge screw system in order to link bone cement to the surrounding bone tissues to avoid bone cement loosening and displacement during or after operation. The key technology was that after the targeted placement of the bone cement bridge screw in IVC, bone cement would be slowly released through the lateral hole at the front of the screw so that the injection pressure of bone cement was smaller, and meanwhile, the screw remained in the vertebral body to link bone cement with normal bone tissues and the pedicle. In this way, the bone cement screw acted as a “bridge” linking bone cement to surrounding tissues, even to the toughest pedicle to enhance mechanical fusion and avoid bone cement loosening and displacement. The tailless design of the screw also allowed the bone cement screw to be fully positioned in the bone structure and less likely to wear away muscle and other soft tissues while acting as a bridge during movement. At the end of the 2-year follow-up, none of the 42 patients had complications such as loosening, displacement and fracture of the bone cement screw, none had delayed bone cement loosening or displacement or skin or soft tissue wear or discomfort caused by the screw. In terms of the main measurement indicators, including VBI, bisegmental Cobb angle, VAS pain score, and ODI function score, the PVP-bone cement bridge screw system combined therapy had much better effects than the PVP-PPP combined therapy.
Compared with the PVP-PPP combined therapy, the PVPbone cement bridge screw system combined therapy also had great advantages in terms of surgical difficulty. The average operation duration of the screw group was 52.07 ± 9.90 minutes (range, 36–65 minutes) and its average bone cement injection volume was 4.43 ± 0.89 mL (range, 2.5–6 mL), while the average operation duration of the PPP group was 85.52 ± 10.78 minutes (range, 70–115 minutes) and its average bone cement injection volume was 4.98 ± 0.67 mL (range, 4–6 mL). The statistical analysis showed that the PVP-bone cement bridge screw system combined therapy had a far shorter operation duration than the PVP-PPP combined therapy, and far less bone cement volume. Based on our treatment experience, the greatest technical difficulties in PPP surgery were the accuracy of bone cement trocar displacement and prevention of bone cement leakage, which could lead to severe complications. First of all, it is a must to ensure the trocar is accurately placed into IVC, and secondly, the intactness of the 4 walls of the pedicle must be ensured during the operation because damage to the inner or lower wall may lead to leakage from the spinal canal or nerve root foramen during the subsequent injection of bone cement, thus resulting in symptoms of nerve injury. In this case, surgeons usually have to perform open surgery to remove the bone cement that compresses the nerve. Tomasian et al. [37] reported that bone cement tended to be distributed in the spinal canal during PPP surgery due to its low impedance. The study conducted by Liu et al. [38] revealed that the incidence of cement leakage was higher in PVP-PPP (29.4%) compared to PVP alone (15.4%). In order to avoid the aforesaid leakages of bone cement, Wang et al. [39] even attempted robots in PPP to ensure safety. However, such leakages of bone cement barely occur in bone cement bridge screw operation, and the operation is easy to operate and safer.
This study, as the first and early clinical retrospective study of the PVP-bone cement bridge screw system combined therapy and the PVP-PPP therapy for unstable KD, has the following deficiencies. First, all the patients included in this study had the lesion in the single vertebral body, but there were also patients with the lesion in multiple vertebral segments in clinical practice, so the results of this study cannot be extensively applied to patients with multivertebral KD for the time being. Second, although this paper has the largest sample size so far among the studies of its kind, 119 patients are still a small sample size, which may limit the universality of the results of this study. Studies of a larger sample size are necessary. Moreover, this study cannot exclude potential interference factors such as the surgeon’s habits and surgical conditions. Fully randomized controlled studies, longer follow-up and multicenter studies are still needed in the future to ultimately lay a solid clinical data basis for the promotion of the bone cement bridge screw system.
CONCLUSION
This 2-year follow-up study on 119 patients showed that compared with the PVP-PPP combined therapy, the PVP-bone cement bridge screw system combined therapy had better mid-and short-term treatment efficacy in patients with unstable KD, could more effectively avoid bone cement loosening and displacement, quickly relieve pain, restore vertebral body height and improve kyphosis, but its long-term efficacy needs further research.
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