Psoas Major Swelling Grade Affects the Clinical Outcomes after OLIF: A Retrospective Study of 89 Patients
Related Experiment Video
Updated: Jul 27, 2026
Three-dimensional Navigation-guided, Prone, Single-position, Lateral Lumbar Interbody Fusion Technique
Published on: July 15, 2021
Zefeng Song1, Wanyan Chen1, Guangye Zhu1
1First Clinical Medical College, Guangzhou University of Chinese Medicine, Guangzhou, China.
Objects:
Oblique lumbar interbody fusion (OLIF) has gained increasing popularity recently. However, complications resulting from intraoperative retraction of psoas major (PM) sometimes occur. The aim of this study is to evaluate the degree of PM swelling by developing a scoring system called the Psoas Major Swelling Grade (PMSG), and to investigate the correlation between the PMSG and clinical outcomes after OLIF.
Methods:
Patients who underwent L4-5 OLIF at our hospital from May 2019 to May 2021 were reviewed and all data were recorded. The extent of postoperative PM swelling was determined by calculating the percentage of change in the PM area before and after surgery on MRI and divided into three grades subsequently. Swelling within the range of 0% to 25% was defined as grade I, 25%-50% was grade II, and more than 50% was grade III. All patients were grouped into the new grade system and followed up for at least 1 year, during which the visual analog scale (VAS) and Oswestry disability index (ODI) scores were recorded. Categorical data were analyzed using chi-square and Fisher's exact tests, while continuous variables were assessed with one-way ANOVA and paired t-tests.
Results:
Eighty-nine consecutive patients were enrolled in this study, with a mean follow-up duration of 16.9 months. The proportion of female patients in the PMSG I, II, and III groups was 57.1%, 58.3%, and 84.1%, respectively (p = 0.024). Furthermore, the total complication rate was 43.2% in the PMSG III group, significantly higher than 9.5% and 20.8% in the PMSG I and II groups (p = 0.012). The incidence of thigh paraesthesia was also considerably higher in the PMSG III group at 34.1% (p = 0.015), compared to 9.5% and 8.3% in the PMSG I and II groups. Among the patients, 12.4% exhibited a teardrop-shaped PM, with the majority (90.9%) belonging to the PMSG III group (p = 0.012). Additionally, the PMSG III group demonstrated a higher estimated blood loss (p = 0.007) and significantly worse clinical scores at the 1-week follow-up assessment (p < 0.001).
Conclusion:
PM swelling adversely affects the OLIF prognosis. Female patients with teardrop-shaped PM are more likely to develop swelling after OLIF. A higher PMSG is associated with a higher complication rate of thigh pain or numbness and worse short-term clinical outcomes.
Insights
A new Psoas Major Swelling Grade (PMSG) system shows that increased psoas major muscle swelling after oblique lumbar interbody fusion (OLIF) is linked to higher complication rates and worse patient outcomes. Female patients with a teardrop-shaped psoas major are more prone to swelling.
Area of Science:
- Spine Surgery
- Orthopedics
- Radiology
Background:
- Oblique lumbar interbody fusion (OLIF) is increasingly used for spinal fusion.
- Intraoperative retraction of the psoas major (PM) muscle during OLIF can lead to complications.
- Quantifying PM swelling is crucial for understanding its impact on surgical outcomes.
Purpose of the Study:
- To develop and validate a scoring system, the Psoas Major Swelling Grade (PMSG), to quantify PM swelling after OLIF.
- To investigate the correlation between PMSG and clinical outcomes, including complications and functional scores, following OLIF.
Main Methods:
- A retrospective review of patients who underwent L4-L5 OLIF between May 2019 and May 2021.
- Postoperative PM swelling was assessed using MRI, calculating the percentage change in PM area, and categorized into three grades (I, II, III).
- Clinical outcomes, including visual analog scale (VAS) and Oswestry disability index (ODI) scores, were recorded at a minimum 1-year follow-up.
Main Results:
- Higher PMSG grades were significantly associated with a higher proportion of female patients (84.1% in Grade III) and increased complication rates (43.2% in Grade III).
- Thigh paresthesia incidence was significantly higher in the PMSG III group (34.1%).
- A teardrop-shaped PM was observed in 12.4% of patients, predominantly in the PMSG III group (90.9%), with higher blood loss and worse short-term clinical scores.
Conclusions:
- PM swelling negatively impacts OLIF prognosis.
- Female patients with a teardrop-shaped PM are at higher risk for developing swelling post-OLIF.
- Elevated PMSG correlates with increased complications (thigh pain/numbness) and poorer short-term clinical outcomes.
