Clinical efficacy and radiological outcomes of a novel screw placement technique for the treatment of traumatic thoracolumbar vertebral fractures under navigation guidance

Abstract

Objective

In this retrospective study, we aimed to evaluate the feasibility, safety, and effectiveness of percutaneous posterior pedicle screw fixation (PPSF) using the FFM(fixed-axis pedicle screws at the injured vertebra and the vertebra above, and multiaxial pedicle screws at the vertebra below) fixation configuration for traumatic thoracolumbar fractures (TLFs) in comparison with conventional percutaneous PPSF and FFM via the Wiltse approach.

Methods

A total of 102 patients with traumatic TLF who were treated between January 2020 and October 2023 were included and divided into three groups: FFM group (percutaneous PPSF using the FFM fixation configuration), FMF group (conventional percutaneous PPSF with multiaxial screws at the fractured vertebra), and Wiltse group (FFM via Wiltse approach). Radiological and clinical outcomes were assessed at pre-operative, postoperative, and follow-up intervals. Perioperative indicators, such as operative time, blood loss, and incision length, were also recorded.

Results

Demographic characteristics were similar among the three groups. At 1 week postoperatively, the FFM group achieved significantly better radiological outcomes than the FMF group, with similar values to the FFM via Wiltse group: VWA (FFM: 6.01 ± 1.96°, FMF: 9.39 ± 2.06°, Wiltse: 6.29 ± 1.27°), AVBH (FFM: 91.26 ± 3.10%, FMF: 85.35 ± 6.40%, Wiltse: 90.54 ± 5.58%), VBI (FFM: 93.45 ± 4.89%, FMF: 88.27 ± 6.64%, Wiltse: 92.96 ± 3.58%) (P < 0.01 for FFM vs FMF; P > 0.05 for FFM vs Wiltse). At the latest follow-up, correction loss of VWA, AVBH, and VBI was significantly lower in the FFM group (1.83 ± 0.62°, 4.70 ± 1.00%, 4.88 ± 3.74%) and FFM via Wiltse group (1.99 ± 0.65°, 4.83 ± 1.19%, 5.28 ± 3.15%) groups than in the FMF group (2.55 ± 0.88°, 6.01 ± 0.81%, 6.57 ± 2.98%) (P < 0.05), with no significant differences between FFM and Wiltse groups (P > 0.05).At 1 week, the FFM and FMF groups reported significantly lower VAS and ODI scores than the Wiltse group (VAS: 2.1 ± 0.8 and 2.0 ± 0.7 vs. 2.7 ± 0.7; ODI: 35.3 ± 11.1 and 38.1 ± 10.0 vs. 44.3 ± 10.7; P < 0.05). No functional differences were noted among groups at later follow-up. The FFM and FMF groups had shorter incisions, operative time, reduced blood loss, and shorter hospital stays compared to the Wiltse group (P < 0.01).

Conclusion

Compared to the FMF configuration, it provides superior radiological outcomes (VWA, AVBH, VBI); the FFM group also reduces blood loss and trauma, compared to the FFM via Wiltse approach group. The FFM configuration for percutaneous PPSF is an effective, minimally invasive technique for managing traumatic TLFs.

Trial registration

Ethics Committee of the General Hospital of the Central Theater Command [2025]066–01, Retrospectively registered. Date of registration: February 24, 2025.

Introduction

The thoracolumbar junction (TLJ, T11–L2) is a critical transitional zone of the spine, which, due to its complex mechanical stress, is highly susceptible to fractures, with approximately 90% of spinal fractures occurring in this area [1–4]. These fractures are typically caused by low-energy trauma in the osteoporotic elderly, or by high-energy trauma (e.g., motor vehicle accidents or falls) in young and middle-aged patients [2, 4]. Vertebral plasty can be applied to treat mild vertebral fracture deformity, mainly aiming to relieve back pain and restore partial vertebral height [5, 6]. Regarding young and middle-aged patients with high-energy trauma, open posterior pedicle screw fixation (PPSF) is advocated [7, 8]. Open PPSF has long been considered the standard treatment for traumatic thoracolumbar fractures (TLFs) [7, 8]. Although open PPSF can achieve superior biomechanical fixation by stabilizing vertebral fractures, these techniques require extensive muscle dissection, resulting in a higher occurrence of morbidities, such as infection and back pain [7–9].

In recent years, minimally invasive spinal surgery has advanced rapidly [9, 10]. Pedicle screws can be inserted through the paraspinal sacrospinalis-splitting approach introduced by Wiltse [10, 11]. PPSF via the Wiltse approach can reduce soft tissue trauma compared to the traditional open operation [11]. Because traumatic TLFs in young and middle-aged individuals are associated with severe vertebral fracture deformity, long-segment PPSF via the Wiltse approach is used to achieve better fracture reduction [12, 13]. However, preserving the motion segments is a crucial principle in spinal surgery. Consequently, it is essential to limit the number of fusion segments while enhancing the effectiveness of instrumentation [13, 14]. Several studies have investigated the effects of short-segment PPSF on traumatic TLFs. Park et al. found that fixed-axis pedicle screws at the fractured vertebra (above and below) combined with multiaxial pedicle screws at the fractured vertebra can also achieve superior fracture reduction compared to long-segment PPSF [15]. Moreover, short-segment PPSF can also be applied to treat traumatic TLFs efficiently with less blood loss and fast recovery [13, 14].

Percutaneous PPSF is a minimally invasive technique that reduces procedure related complications [16, 17]. Our team has conducted multiple studies on its application for traumatic TLFs [18–21]. However, using multiaxial screws at the injured vertebra in short-segment fixation often fails to provide sufficient support, leading to correction loss [22]. In cases with endplate injury and severe vertebral compression, current techniques remain limited in maintaining long-term vertebral height and alignment [23]. These shortcomings highlight the need to explore alternative screw configurations that offer improved biomechanical stability and sustained correction.

Postoperative loss of vertebral height and angular correction remains a concern.We proposed an alternative configuration, with fixed-axis pedicle screws at the injured vertebra and the vertebra above, and multiaxial pedicle screws at the vertebra below (FFM; percutaneous PPSF using the FFM fixation configuration) (illustration in Fig. 1). This surgical technique aimed to improve vertebral height restoration and kyphotic correction using the leverage principle. To our knowledge, few studies have systematically evaluated the clinical and radiological outcomes of percutaneous FFM fixation, particularly in comparison with other minimally invasive surgery. Therefore, a retrospective analysis was performed to evaluate the feasibility, safety, and effectiveness of short-segment PPSF using FFM compared to conventional percutaneous PPSF and FFM via the Wiltse approach for addressing traumatic TLFs.

Fig. 1.

New Type of pedicle screw internal fixation method. (Yellow represents fixed-axis pedicle screws, and purple represents multiaxial pedicle screws)

Methods

Inclusion and exclusion criteria

The inclusion criteria for this study were as follows: (1) Patients aged between 18 and 60 years; (2) Single-segment traumatic thoracolumbar fractures located between T11 and L2; (3) AO Spine classification Type A3 or A4; (4) Intact bilateral pedicles at the fractured vertebra; (5) No or minimal neurological deficit (Frankel Grade D or E); (6) Time from injury to surgery ≤ 14 days; (7)Minimum follow-up duration of 12 months, with complete clinical and radiological data. The exclusion criteria were as follows: (1) Pathological fractures (e.g., spinal tuberculosis, primary or metastatic tumors, infection); (2) Involvement of more than two contiguous vertebrae; (3) Osteoporotic fractures (T-score < − 2.5 confirmed by DEXA scan); (4) Previous spinal trauma or history of spinal surgery at the same segment; (5) Polytrauma with life-threatening organ injuries; (6) Active pregnancy; (7) Severe cardiopulmonary dysfunction or coagulation disorders.

Patient population

In this retrospective study, we reviewed patients with thoracolumbar fractures treated at the Central Theater Command General Hospital of PLA between January 2019 and May 2023 using three distinct surgical approaches. Based on the inclusion criteria, 112 patients were included in this study, including 87 with type A3 fractures and 28 with type A4 fractures. In accordance with the exclusion criteria, four cases of type A3 and six cases of type A4 were excluded from the analysis. The remaining 102 patients were divided into three groups based on the surgical approach used: the FFM group (percutaneous PPSF using the FFM fixation configuration), the FMF group (conventional percutaneous PPSF with multiaxial screws at the fractured vertebra), and the Wiltse group (Wiltse-approach PPSF with the FFM fixation configuration).

The Wiltse-approach group was included because the FFM configuration was originally applied through this open approach. The percutaneous FFM technique was later developed as a minimally invasive adaptation, retaining the same screw configuration. Including both allows comparison between open and percutaneous applications of FFM, helping to clarify whether the benefits are due to surgical approach.

The study was approved by the Ethics Committee of the Central Theater Command General Hospital of PLA and adhered to the principles outlined in the Declaration of Helsinki ([2025]066–01).

Surgical technique

All surgeries were performed by the same team under the supervision of an experienced chief surgeon. After the induction of general anesthesia, the patient was positioned prone on a Jackson surgical table, with the abdomen suspended on pads placed at the chest and anterior–superior iliac spines. In the FFM group, the target vertebra was identified using O-arm navigation. The navigation system was calibrated, and the entry points were marked approximately 1.5 cm lateral to the outer margins of the pedicles at the injured and adjacent vertebrae.

Six Jamshidi needles were then inserted into the pedicles under real-time navigation guidance to ensure that each needle followed the predesigned trajectory. Once the needle positions were confirmed via the navigation system, the needle cores were removed, and guidewire were inserted through the needle cores to maintain the guidewire positions within the vertebrae. After determining the appropriate screw sizes and positions (Fig. 2B), fixed-axis pedicle screws were inserted into the vertebrae above the injured segment and into the injured vertebra itself. Subsequently, multiaxial screws were placed in the vertebrae below the injured segment. The navigation system was used to verify the correct placement and trajectory of each screw, ensuring optimal alignment and positioning (Fig. 2A).

Fig. 2.

Step-by-step depiction of the percutaneous PPSF procedure using the FFM configuration. B Tapping along the screw path, followed by insertion of fixed-axis pedicle screws above and at the injured vertebra, and multiaxial pedicle screws below. C Selection and shaping of an appropriately sized connecting rod to match the physiological curvature of the fractured segment. D, E Insertion of the rod and tightening of the head and tail screws. F The physiological curvature of the spine is restored. G, H A specially designed retractor between fixed-axis and multiaxial screws to lock their position relative to the rod. I Restoration of vertebral height using a lever mechanism

After determining the appropriate physiological curvature, rods of an appropriate length were selected and contoured to match the physiological curvature of the fractured segment (Fig. 2C). The rods were then inserted (Fig. 2D), the nuts on both the cranial and caudal screws were tightened (Fig. 2E), and the normal physiological curvature of the spine was restored (Fig. 2F). A specially designed retractor was placed between the fixed-axis and multiaxial screws to lock the position of the fixed-axis screw relative to the rod (Fig. 2G, H). Finally, the leverage principle was used to restore the vertebral height of the injured vertebrae (Fig. 2I).

The FMF and Wiltse processes were performed as described as previously [24, 25]. The internal fixation stabilization system was provided by Shandong Weigao Company located in China. Following surgery, all patients routinely received prophylactic antibiotics for a duration of 48 h, and the sterile dressing on the incision was changed every 2 days until the sutures were removed. Patients were motivated to begin physical activities while wearing a brace; nevertheless, strenuous and heavy activities were Limited for up to 3 months after surgery.

Clinical assessment

Imaging evaluation indicators included measurements of the sagittal cobb angle (SCA), vertebral wedge angle (VWA), anterior vertebral body height (AVBH), vertebral body index (VBI), and spinal canal encroachment rate (SCER). The measurement methods for the SCA, VWA, AVBH, and VBI are illustrated in Fig. 3a. CT scans were used to assess the SCER, which served as an indicator of spinal canal decompression (Fig. 3b). The loss of correction in the SCA was calculated using the following formula: (SCA at 1 week postoperatively – SCA at the latest follow-up)/SCA at 1 week postoperatively. The same formula was applied to calculate the loss of correction for the AVBH, VWA, VBI, and SCER. Perioperative indicators included operation time, blood loss, incision length, and length of postoperative hospital stay. Clinical evaluation indicators assessed the functional status pre-operatively and at various follow-up intervals (1 week, 3 months, and the latest follow-up) using the Visual Analogue Scale (VAS) and Oswestry Disability Index (ODI) questionnaires [26]. The VAS and ODI scores were recorded during each orthopedic outpatient follow-up visit. Complications such as infection, screw or rod breakage, and screw loosening were also noted. All data measurements were performed independently by two observers, with the final values being the average of the measurements.

Fig. 3.

Radiological assessment parameters. a SCA: The angle between the superior endplate of the upper vertebra and the inferior endplate of the lower vertebra. VWA: The angle measured between the lines drawn along the superior and inferior endplates of the compressed vertebra. AVBH: h1/[(h2 + h3)/2] × 100%. VBI: The ratio of anterior to posterior vertebral height (VBI = [h1/h4] × 100%). (b) SCER = w2/[(w1 + w3)/2] × 100%

Statistical analyses

Statistical analysis was performed using SPSS 27.0 software (SPSS Inc., Chicago, IL, USA). Continuous variables are presented as the mean ± standard deviation, whereas categorical variables are presented as frequencies and percentages. Analytical methods included Kruskal–Wallis rank-sum test, one-way analysis of variance, and chi-square test. When conducting multiple pairwise comparisons, Bonferroni correction was applied to reduce the risk of Type I errors. These statistical methods were used to assess significant differences between different groups or within groups. A P-value < 0.05 was considered statistically significant.

Results

Demographic data

A total of 102 patients were included in this study based on the established inclusion and exclusion criteria. The cohort consisted of 35 patients in the FFM group, including 24 males (68.57%) and 11 females (31.43%), with a mean age of 39.7 ± 5.4 years. The FMF group included 36 patients (17 men [47.22%] and 19 women [52.78%]), with a mean age of 37.1 ± 6.3 years. The Wiltse group consisted of 31 patients with 16 males (51.61%) and 15 females (48.39%), with a mean age of 38.3 ± 5.6 years. Demographic characteristics such as age, sex, body mass index (BMI), bone mineral density (BMD), cause of injury, fracture level, thoracolumbar injury classification and severity (TLICS) score, load sharing classification (LCS) score, and follow-up duration were collected and compared among the three groups. No significant differences were observed across these variables (Table 1).

Table 1.

Comparison of demographic data between the three groups

Demographic data between the three groups
Characteristics	FFM (n = 35)	FMF (n = 36)	Wiltse (n = 31)	P-value
Age (years)	39.7 ± 5.4	37.1 ± 6.3	38.3 ± 5.6	0.167
Sex (male) %	24 (68.57%)	17 (47.22%)	16 (51.61%)	0.164
BMI	23.6 ± 0.5	23.7 ± 0.5	23.1 ± 1.1	0.094
BMD	–0.50 ± 0.30	–0.50 ± 0.28	–0.57 ± 0.29	0.544
Cause of injury				0.983
Fall from height	13	12	11
Traffic accidents	15	18	14
Other	7	6	6
Fracture level				0.786
T11	1	2	2
T12	11	10	9
L1	11	17	12
L2	12	7	8
TLICS score				0.851
4	7	9	6
5	28	27	25
LSC score				0.937
3	3	2	1
4	6	5	3
5	10	10	9
6	10	13	14
7	6	6	4
Time of last follow-up (month)	15.4 ± 2.1	15.2 ± 2.0	14.9 ± 2.1	0.503

Data are presented as the mean ± standard deviation, and categorical variables are presented as frequencies and percentages

BMI Body mass index

^*FFM vs. FMF

^#represents FFM vs. Wiltse

^†represents FMF vs. Wiltse

P-values < 0.05 represent significance

Perioperative indicators

The perioperative variables were examined to identify differences among the three groups. The average surgical incision length was 9.1 ± 1.1 cm, the average surgical duration was 96.9 ± 10.3 min, the average intraoperative blood loss was 69.0 ± 19.3 ml, and the average postoperative hospital stay was 9.6 ± 2.5 days. No significant differences were observed between the FFM and FMF groups in terms of the parameters of surgical incision length, surgical duration, intraoperative blood loss, and postoperative hospital stay (P > 0.05). However, the FFM and FMF groups showed significant differences in these parameters when compared to the Wiltse group (P < 0.05) (Table 2).

Table 2.

Comparison of the general surgical parameters among the three groups

Comparison of the general surgical parameters among the three groups
Characteristics	FFM	FMF	Wiltse	*P-value	#P-value	†P-value
Incision length (cm)	8.8 ± 1.1	8.7 ± 0.9	9.8 ± 1.0	0.91	< 0.01	< 0.01
Surgical duration	104.8 ± 7.7	102.3 ± 11.2	104.6 ± 7.1	0.46	< 0.01	< 0.01
Intraoperative blood loss	65.1 ± 15.1	60.0 ± 15.9	83.9 ± 18.7	0.40	< 0.01	< 0.01
Postoperative hospital stay	9.0 ± 2.8	9.0 ± 2.1	11.1 ± 2.2	1.00	< 0.01	< 0.01

Data are represented as the mean ± standard deviation

^*FFM vs. FMF

^#represents FFM vs. Wiltse

^†represents FMF vs. Wiltse

P-values < 0.05 represent significance

Radiologic outcomes

Pre-operatively, no statistically significant differences were observed among the three groups for variables in the SCA, VWA, AVBH, VBI, and SCER (P > 0.05). Postoperatively, all three groups exhibited significant improvements in the SCA, VWA, AVBH, VBI, and SCER compared to pre-operative values. Notably, at the 1-week postoperative time point, significant differences in VWA, AVBH, and VBI were observed between the FFM and Wiltse groups compared to the FMF group (P < 0.01). However, no significant differences in SCA and SCER were observed among the three groups. At both the 3-month and the latest follow-up, the FFM and Wiltse groups showed significant improvements in VWA, AVBH, and VBI compared to the FMF group (P < 0.05). In contrast, no significant differences were observed among the groups for SCA and SCER (P > 0.05) (Table 3).In the latest follow-up, there was no significant difference in the correction loss rates of the VWA, AVBH, and VBI between the FMF and Wiltse groups (P > 0.05). However, the correction loss rates of VWA, AVBH, and VBI in the FFM and Wiltse groups were significantly lower than those in the FMF group (P < 0.05) (Table 3).

Table 3.

Comparison of radiologic evaluation indicators between the three groups

Comparison of radiologic evaluation indicators between the three groups
Characteristics	FFM	FMF	Wiltse	*P-value	#P-value	†P-value
SCA (◦)
Pre-operation	19.31 ± 2.72	19.27 ± 2.65	19.81 ± 2.74	1.00	0.74	0.70
1 week postoperatively	7.26 ± 2.08	7.44 ± 2.01	7.29 ± 1.95	0.92	1.00	0.95
3 months postoperatively	8.34 ± 2.09	8.72 ± 1.98	8.39 ± 1.61	0.68	0.97	0.76
Latest follow-up	9.91 ± 1.84	9.94 ± 1.85	9.87 ± 1.43	0.96	0.99	0.98
Correction loss (last follow-up)	2.66 ± 0.73	2.50 ± 0.97	2.58 ± 1.15	0.77	0.94	0.93
VWA (◦)
Pre-operation	18.66 ± 2.46	18.14 ± 2.47	18.90 ± 2.60	0.66	0.92	0.43
1 week postoperatively	6.01 ± 1.96	9.39 ± 2.06	6.29 ± 1.27	< 0.01	0.79	< 0.01
3 months after surgery	7.06 ± 1.76	10.58 ± 2.02	7.48 ± 1.29	< 0.01	0.58	< 0.01
Latest follow-up	7.83 ± 1.62	11.94 ± 1.82	8.23 ± 1.09	< 0.01	0.56	< 0.01
Correction loss (last follow-up)	1.83 ± 0.62	2.55 ± 0.88	1.94 ± 0.63	< 0.01	0.82	< 0.01
AVBH (%)
Pre-operation	63.98 ± 6.40	62.83 ± 6.56	63.04 ± 6.17	0.73	0.82	0.99
1 week postoperatively	91.26 ± 3.10	85.35 ± 6.40	90.54 ± 5.58	< 0.01	0.84	< 0.01
3 months after surgery	87.71 ± 2.85	82.00 ± 6.41	86.99 ± 5.69	< 0.01	0.86	< 0.01
Latest follow-up	86.56 ± 2.93	79.34 ± 6.39	85.78 ± 5.68	< 0.01	0.81	< 0.01
Correction loss (last follow-up)	4.70 ± 1.00	6.01 ± 0.81	4.75 ± 0.80	< 0.01	0.97	< 0.01
VBI (%)
Pre-operation	58.52 ± 6.71	57.74 ± 7.07	57.67 ± 6.40	0.88	0.87	1.00
1 week postoperatively	93.45 ± 4.89	88.27 ± 6.64	92.96 ± 3.58	< 0.01	0.92	< 0.01
3 months after surgery	90.37 ± 4.77	84.99 ± 5.88	89.67 ± 4.02	< 0.01	0.83	< 0.01
Latest follow-up	88.57 ± 3.96	81.69 ± 5.80	87.96 ± 4.04	< 0.01	0.86	< 0.01
Correction loss (last follow-up)	4.88 ± 3.74	6.57 ± 2.98	4.99 ± 2.62	< 0.05	0.99	< 0.05
SCER
Pre-operation	73.89 ± 4.93	72.71 ± 4.04	74.13 ± 4.11	0.50	0.97	0.39
1 week postoperatively	92.58 ± 3.12	91.89 ± 4.13	92.70 ± 3.61	0.70	0.99	0.63
3 months after surgery	92.35 ± 3.13	91.71 ± 4.14	92.46 ± 3.57	0.73	0.99	0.67
Latest follow-up	92.13 ± 3.15	91.53 ± 4.14	92.34 ± 3.63	0.77	0.97	0.64
Correction loss (last follow-up)	0.45 ± 0.15	0.36 ± 0.21	0.36 ± 0.24	0.14	0.20	0.99

Data are represented as the mean ± standard deviation

SCA Sagittal cobb angle, VWA Vertebral wedge angle, AVBH Anterior vertebral body height, VB: Vertebral body index, SCER Spinal canal encroachment rate

^*FFM vs. FMF

^#represents FFM vs. Wiltse

^† represents FMF vs. Wiltse

P-values < 0.05 represent significance

Clinical outcomes

The VAS scores of all three groups showed significant improvement postoperatively. There were no significant differences in the VAS scores among the three groups at the pre-operative (P > 0.05). However, at the 1-week follow-up, the VAS scores in the FFM and FMF groups were significantly lower than those in the Wiltse group (P < 0.05). At both the 3-month and latest follow-ups, no significant differences in VAS scores were observed among the three groups (P > 0.05). Similarly, the ODI scores of all three groups showed significant improvement postoperatively. No significant differences in ODI scores were observed at the pre-operative and 1-week follow-ups (P > 0.05); however, at the 1-week follow-up, the ODI scores in the FFM and FMF groups were significantly lower than those in the Wiltse group (P < 0.05). At both the 3-month and latest follow-ups, no significant differences in ODI scores were found among the three groups (P > 0.05) (Table 4).

Table 4.

Comparison of the VAS and ODI scores among the three groups

Comparison of the VAS and ODI scores among the three groups
Characteristics	FFM	FMF	Wiltse	*P-value	#P-value	†P-value
VAS score
Pre-operation	7.4 ± 1.4	7.5 ± 1.6	7.1 ± 1.4	0.96	0.75	0.59
1 week postoperatively	2.1 ± 0.8	2.0 ± 0.7	2.7 ± 0.7	0.96	< 0.05	< 0.05
3 months postoperatively	1.2 ± 0.6	1.5 ± 0.6	1.5 ± 0.7	0.10	0.10	1.00
Last follow-up	0.7 ± 0.4	0.8 ± 0.4	0.9 ± 0.3	0.96	0.99	0.98
ODI score (%)
Pre-operation	84.5 ± 7.2	84.2 ± 6.6	85.0 ± 7.8	0.99	0.95	0.89
1 week postoperatively	35.3 ± 11.1	38.1 ± 10.0	44.29 ± 10.7	0.52	< 0.01	< 0.05
3 months after surgery	13.0 ± 7.2	13.5 ± 7.1	13.3 ± 7.5	0.87	0.94	0.98
Last follow-up	5.1 ± 4.5	5.4 ± 5.3	5.7 ± 5.0	0.98	0.87	0.95

Data are represented as the mean ± standard deviation

ODI Oswestry Disability Index, VAS Visual Analogue Scale

^*FFM vs. FMF

^#represents FFM Vs. Wiltse

^†represents FMF vs. Wiltse

P-values < 0.05 represent significance

Complications

None of the three groups experienced complications, such as nerve injury or cerebrospinal fluid leakage, following surgery. In the Wiltse group, postoperative infections were reported in three patients, whereas no infections were observed in the other two groups. During the postoperative follow-up, there was 1 screw breakage each in the Wiltse and FFM groups, the failure rate was 3.23% and 2.86%, respectively.The patient selected conservative treatment and regular follow-up visits until the internal fixation was removed. No screw fractures or loosening events were reported in the other two groups. There were no significant differences in the incidence of complications between the two groups (Table 5) (P > 0.05). Typical case images of the FFM fixation configuration are shown in Fig. 4. The representative cases of the FMF fixation group and the FFM via Wiltse fixation group are presented in Supplementary Figs. 1 and 2.

Table 5.

Comparison of the postoperative complications among the three groups

Comparison of the postoperative complications among the three groups
Characteristics	FFM (n = 35)	FMF (n = 36)	Wiltse (n = 31)	*P-value	#P-value	†P-value
Complications				1.00	0.849	0.264
Infection	0	0	3
Hardware breakage	1	0	1
Pedicle screw loss	0	0	0

Data are represented as the mean ± standard deviation

^*FFM vs. FMF

^#represents FFM vs. Wiltse

^†represents FMF vs. Wiltse

P-values < 0.05 represent significance

Fig. 4.

A 32-year-old male patient with an L1 burst fracture underwent FFM fixation. Preoperative lumbar X-rays (a, b) and CT scans (c, d) revealed an L1 AO type A3 fracture with spinal canal encroachment. MRI confirmed a fresh fracture of the L1 vertebra (e). Postoperative X-rays (f, g) and CT scans (h-j) taken one week later demonstrated satisfactory restoration of the injured vertebral height and successful correction of kyphosis

Discussion

In this retrospective study, we compared percutaneous PPSF with FMF configuration, and FFM via the Wiltse approach for the treatment of traumatic TLFs. Before percutaneous pedicle screw fixation, PSF via the Wiltse approach has been widely used to treat traumatic TLFs as a standard minimally invasive surgical option [9, 10, 27]. With the advancement of surgical techniques, percutaneous PPSF has been developed for the treatment of traumatic TLF. A series of modified PPSF procedures have been reported by our hospital [18–21], however, inadequate vertebral height restoration and incomplete correction of local kyphosis were often observed during follow-up [18–21]. In this study, we found that the radiological parameters, including the VWA, AVBH, and VBI, were significantly corrected in patients who received FFM configuration. Our preliminary findings showed that percutaneous PPSF with an FFM fixation configuration can effectively recover and maintain the height of fractured vertebrae and prevent further correction loss. Moreover, it can also reduce surgical trauma.Therefore, percutaneous PPSF with an FFM fixation configuration might serve as a secure and efficient alternative for the treatment of traumatic TLFs.

In this study, we used a modified FFM using the leverage technique. This procedure comprises two main steps. First, fixed-axis screws are percutaneously implanted parallel to the superior endplates of the compressed and above vertebrae, and multiaxial pedicle screws are also percutaneously implanted at the below vertebra. Subsequently, two rods are placed on either side, and the nuts of the cranial and caudal screws were then tightened. The physiological curvature of the thoracic and lumbar segments was restored using this surgical maneuver. Second, a specially designed retractor was positioned between the fixed-axis and multiaxial screws perpendicular to the rod. The retractor was then applied to lock the position of the fixed-axis screw relative to the rod. During tightening of the fixed-axis screw, the screw tail shifts caudally while the screw tip elevates toward the cranial side, thereby reducing the compressed vertebra. The FFM has several advantages. First, fixed-axis screws can effectively transmit the lifting force to the superior endplate of the compressed vertebrae. The fixed-axis screws were vertical to the rods after the nuts were tightened during the tightening process of the nail cap. Second, superior biomechanical stability was observed in FFM with the addition of long-length pedicle screws at the fracture level without compromising the benefits of SSIF. The application of a navigation system can significantly improve the accuracy of screw placement and increase the length of the pedicle screws. PPSF with the aid of a navigation system allows for real-time visualization of the screw trajectory and its relationship to surrounding structures, thereby reducing the risk of lateral wall perforation and subsequent vascular injury. Third, FFM is particularly suitable for traumatic TLF caused by high-energy injury trauma. FFM can sufficiently maintain reduction and prevent further loss of correction. Correction loss often results from postoperative “eggshell” deformity because a defect caused by compressed bone trabeculae cannot be restored. The application of long-length intermediate pedicle screws in FFMs can enhance construct stiffness and reduce the adverse effects associated with the “eggshell” deformity during the fracture healing process [10].

Biomechanically, fixed-axis pedicle screws provide greater stability due to their rigid screw-rod connection, which limits angular motion and enhances load transfer from the rod to the vertebral body. Studies have shown that fixed-axis constructs are more resistant to toggling and micromotion compared to multiaxial screws, offering better vertebral height maintenance and kyphotic angle correction [28]. The leverage mechanics of the FFM configuration further improve fracture reduction and prevent correction loss, particularly in high-energy compression fractures. This enhanced mechanical rigidity and stability make fixed-axis screws ideal for unstable thoracolumbar fractures. Lastly, recent studies suggest that paraspinal muscle integrity significantly affects postoperative alignment stability. Liao et al. reported that greater muscle fatty infiltration correlated with increased kyphosis correction loss [29]. Although the Wiltse approach is less invasive than traditional open surgery, it still involves muscle splitting, unlike the fully percutaneous FFM technique, which better preserves muscle. It suggests that the FFM group might provide superior biomechanical stability compared to the FFM via Wiltse group.

A total of 102 patients with traumatic TLF received treatment using three distinct types of internal fixation. The radiological outcomes of these patients were evaluated in this retrospective study. Compared to FMF, FFM and FFM via the Wiltse approach result in superior postoperative correction and maintenance. Initial correction of the VWA, AVBH, and VBI in the FFM group and FFM via Wiltse approach group was significantly improved compared to that in the FMF group. Moreover, the correction losses of the VWA, AVBH, and VBI in the FFM group and FFM via Wiltse approach group were also significantly reduced compared to those in the FMF group at the latest follow-up. However, no significant difference in correction losses was observed between the FFM group and FFM via Wiltse approach group. Compared with previously published studies, multiaxial screws placed at the fractured vertebra have proven insufficient to support severely compressed burst fractures with significant height loss. The postoperative improvements in VBI(85.7 ± 8.3%) and AVBH(83.5 ± 9.0%), reported in those studies were markedly inferior to those achieved with our fixation strategy [30]. This suggests that FFM can better maintain reduction and prevent further correction loss compared to FMF. Previous studies have reported no clear relationship between changes in the SCER and the correction of the kyphotic angle [31]. Neurological recovery is primarily dependent on the severity of spinal cord injury at the moment of trauma [32, 33].

The values of all general parameters (blood loss, incision length, operation duration,and hospital stay) in the FFM via Wiltse approach group were the highest among the three groups; however, no significant differences regarding these parameters were observed between the FFM and FMF groups. Compared with previously published studies, the surgical outcomes of the Wiltse approach in terms of intraoperative blood loss and length of hospital stay were similar to those reported in our Wiltse group. However, both parameters were significantly lower than those observed in the percutaneous PPSF groups in our study [14]. Reduced operation duration and hospital stay are due to reduced paraspinal muscle damage [10]. Using a separate lateral incision, pedicle screws were implanted through blunt dissection between the longissimus and multifidus muscles in the FFM using the Wiltse approach. The lateral incision containing three pedicle screws was longer than those in the FFM and FMF groups. Previous studies have reported that the incidence of PPSF instrumentation failure is 11.7% [8]. However, the incidence of instrumentation failure (3.2%) was reduced compared to that reported in this study, with only 2 case of screw breakage in the FFM group and Wiltse group. We attributed this instrumentation failure to increased stress on the pedicle screw, which might have resulted from the patient’s history of heavy work without the protection of a brace postoperatively.

Postoperative VAS scores for back pain significantly decreased in all three groups compared to preoperative levels, indicating that all surgical techniques effectively alleviated symptoms. At the 1-week follow-up, however, patients in the FMF and FFM groups reported slightly higher VAS scores than those in the Wiltse group. This difference may be attributed to variations in surgical access and the extent of paraspinal muscle disruption. Nevertheless, the difference in early postoperative pain did not persist long-term, as no significant differences in VAS or ODI scores were observed at later follow-ups. Compared with previous studies, the FFM group demonstrated similar improvements in VAS and ODI scores [34].

Limitations

Several limitations should be acknowledged. Firstly, Firstly, this was a retrospective study conducted at a single medical center with a short follow-up duration and a relatively small sample size, which may underestimate long-term complications such as instrumentation failure or adjacent-segment degeneration. Therefore, a large-scale multicenter randomized, prospective study is required in the future. Secondly, underlying variables including disc degeneration, bone density and vertebrae size are diverse. It is necessary to conduct a finite-element study to offset the effect of these confounding variables on the conclusion of this study. Thirdly, the effect of instrumentation removal was not considered in this study. It would be interesting to investigate the long-term functional recovery, including correction loss, deformity prevention and adjacent segment degeneration following instrumentation removal.

Conclusion

The FFM group exerted greater interface strength on the fractured vertebra and improved radiological parameters, including the VWA, AVBH, and VBI, with significantly superior results compared to the FMF group; the FFM group also exhibited reduced blood loss and trauma, enhanced early rehabilitation, and improved rapid relief of back pain compared to the FFM via Wiltse approach group. In conclusion, FFM is a reliable and effective surgical technique for managing traumatic TLF.

Authors’ contributions

K. N.: Data management, writing-original draft. B.H.: Data management, writing-review and editing. F.X. and C.X.: Conceptualization, verification, supervision, project administration. F.X.: Surgical practitioners. Z.W.,Z.T.and L.C.: Investigation, data analysis, and statistics. T.W.and X.W.: Verification, data management. All authors contributed to the article and approved the submitted version.

Funding

This study was funded by the the Wuhan Knowledge Innovation Special Project (2023020201010177) and Hubei Province Health Science and Technology Health Project (WJ2025M049).

Data availability

The data used and/or analyzed in this study can be obtained from the corresponding author upon reasonable request.

Declarations

Ethics approval and consent to participate

The study adheres to the Declaration of Helsinki. Approval was obtained from Clinical Research Ethics Committee of the General Hospital of Central Theater Command (approval number: [2025]066–01). Written informed consent was obtained from all patients.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.