Enlarged posterior column osteotomy plus intervertebral cage strutting for lumbosacral nerve bowstring disease.

BACKGROUND: To explore the surgical outcome of enlarged posterior column osteotomy (EPCO) plus intervertebral cage strutting (ICS) for patients with lumbosacral nerve bowstring disease (BSD). METHODS: The clinical data of 27 patients with BSD that surgically treated with EPCO plus ICS from January 2018 to March 2021 were retrospectively reviewed. Patient demographics including age, gender, body mass index (BMI), duration, length of hospital stay, SF-36 were recorded. Surgical data including operation time, blood loss, surgical level, and complications were recorded. Inter-pedicle distance and regional lumbar lordosis was measured at lateral X-ray at both pre- and postoperative. RESULTS: All patients underwent the operation successfully. EPCO plus ICS was performed at L4-L5 in 9 patients, at L5-S1 in 7 patients, at L4-S1 in 6 patients, at L3-L5 in 5 patients. The mean operation time was 96.3 ± 18.0 min, mean blood loss was 350.0 ± 97.9 mL. Relaxation of thecal sac was noticed after pedicle screw-rod compression bilaterally. The mean decrease of inter-pedicle distance was 0.57 ± 0.18 cm, the mean increase of regional lumbar lordosis was 17.6 ± 6.7 degrees. Relaxation of cauda equina within the thecal sac was noticed at intra-operative after pedicle screw-rod compression bilaterally in all the patients. Most patients achieved neurological function improvement at two-year follow up. CONCLUSIONS: EPCO plus ICS procedure is an effective surgical method for lumbosacral nerve BSD through restoring the coordination between column and cord, visual relaxation of cauda equina within the thecal sac at intraoperative is the key factor in determining the relief of neurological function at postoperative.

Inherited genetic predisposition and imaging concordance in degenerative lumbar scoliosis patients and their descendants.

BACKGROUND: Offspring consistently exhibit similar imaging features as their parents in cases of degenerative lumbar scoliosis (DLS). Nevertheless, the role of genetic factors in the pathogenesis of DLS remains uncertain. METHODS: A prospective analysis was conducted on 35 patients with DLS and their 36 offspring. Genomic DNA was extracted from 71 blood samples for gene mutation analysis using whole exome sequencin. Various demographic and imaging parameters were compared. RESULTS: In 11 pedigrees of the 35 family members with DLS, 13 suspected pathogenic genes were identified. Among the 35 DLS patients, 11/35(31.5%) exhibited susceptibility gene mutations (mutant group), while 24/35(68.5%) had no pathogenic gene mutations (non-mutant group). AVR was more severe in mutant group than that in no-mutant group (p < 0.05). Among the 36 offspring, 11/36(30.6%) cohorts presented susceptibility genes (mutant group), 25/36(69.4%) cohorts presented no pathogenic genes (no-mutant group). More cohorts in the mutant group presented vertebral rotation (72.8%) and scoliosis (45.5%) than those (24%), (12%) in the no-mutant group, respectively (p < 0.05). Among the 36 offspring, 8/36(22.2%) presented scoliosis (study group), they all presented the same scoliosis orientation and apex vertebrae/disc location to their parents, the other 28/36(77.8%) cohorts without scoliosis were enrolled as control group, the mutation rate (62.5%) was higher in study group than that (21.4%) in control group. CONCLUSIONS: Genetic influences are significant in the onset of DLS, with affected families showing similar scoliosis patterns and identical apex vertebrae. Moreover, individuals with genetic mutations tend to have more pronounced vertebral rotation and at a higher risk of developing scoliosis.

Sex-based differences in clinical and radiological presentation of patients with degenerative lumbar scoliosis: a cross-sectional study.

BACKGROUND: To evaluate the sex-based differences in clinical and radiological presentation of patients with degenerative lumbar scoliosis (DLS) and to explore whether the difference is helpful in investigating the etiology and progression of DLS. METHOD: A retrospective review of 199 patients (41 males, 158 females) with DLS was included. Patient demographics including age, gender, bone mineral density were collected. Back and leg pain was assessed by visual analog scale, and general physical condition was assessed by Oswestry Disability Index. Cobb's angle was measured, and direction of scoliosis, position of the superior, inferior and apex vertebrae, number of vertebrae included in the scoliosis, rotation of apex vertebrae (Nash-Mo index), translation of apex vertebrae were recorded. Sagittal longitudinal axis, thoracolumbar kyphosis, lumbar lordosis (LL), pelvic incidence angle (PI), sacral slope, apex of lumbar lordosis and coronal balance distance were measured by whole spine lateral radiographs, and type of coronal imbalance was evaluated in all patients. Fat infiltration rate (FIR) of the paraspinal muscles at the vertebral apex was measured by MRI. RESULT: Compared to female patients, male patients showed more back and leg pain on clinical presentation and smaller Cobb angle, less parietal rotation, larger LL, smaller PI-LL and lower paravertebral muscle FIR on radiologic features. CONCLUSION: Gender differences do exist in DLS patients with regard to clinical and radiological presentation, low back pain was more pronounced in male patients, and scoliosis was more severe in female patients based on this cross-sectional study.

Application of Stand-Alone Oblique Lateral Interbody Fusion in L4-5 Lumbar Diseases.

Lumbar spine diseases often cause lower back pain, lower extremity pain, numbness, and paresthesia. In severe cases, intermittent claudication may occur, affecting the quality of life of patients. Surgery is often required when conservative treatment fails, or when patients' symptoms become unbearable. Surgical treatments include laminectomy and discectomy, as well as interbody fusion. The main purpose of laminectomy and discectomy is to relieve nerve compression; however, recurrence is common due to spinal instability. Interbody fusion improves stability while relieving nerve compression and significantly reduces the risk of recurrence compared to non-fusion surgery. Nonetheless, conventionally posterior intervertebral fusion requires separation of the muscles to expose the operated segment, which causes more trauma to the patient. In contrast, the oblique lateral interbody fusion (OLIF) technique achieves spinal fusion with minimal trauma to the patients and shortens the recovery time. This article introduces procedures of stand-alone OLIF surgery performed in the lumbar spine, providing a reference for other spine surgeons.

Characteristics of the paravertebral muscle in adult degenerative scoliosis with PI-LL match or mismatch and risk factors for PI-LL mismatch.

Objective: Pelvic incidence (PI) minus the lumbar lordosis (LL) angle (PI-LL) correlates with function and disability. It is associated with paravertebral muscle (PVM) degeneration and is a valuable tool for surgical planning of adult degenerative scoliosis (ADS). This study aims to explore the characteristics of PVM in ADS with PI-LL match or mismatch and to identify the risk factors for PI-LL mismatch. Methods: A total of 67 patients with ADS were divided into PI-LL match and mismatch groups. The visual analog scale (VAS), symptom duration, and Oswestry disability index (ODI) were used to assess patients' clinical symptoms and quality of life. The percentage of fat infiltration area (FIA%) of the multifidus muscle at the L1-S1 disc level was measured by using MRI with Image-J software. Sagittal vertical axis, LL, pelvic tilt (PT), PI, sacral slope, and the asymmetric and average degeneration degree of the multifidus were recorded. Logistic regression analysis was done to identify the risk factors for PI-LL mismatch. Results: In the PI-LL match and mismatch groups, the average FIA% of the multifidus on the convex side was less than that on the concave side (P < 0.05). There was no statistical difference of asymmetric degeneration degree of the multifidus between the two groups (P > 0.05). In the PI-LL mismatch group, the average degeneration degree of the multifidus, VAS, symptom duration, and ODI were significantly higher than that in the PI-LL match group, respectively (32.22 ± 6.98 vs. 26.28 ± 6.23 (%), 4.33 ± 1.60 vs. 3.52 ± 1.46, 10.81 ± 4.83 vs. 6.58 ± 4.23 (month), 21.06 ± 12.58 vs. 12.97 ± 6.49, P < 0.05). The average degeneration degree of the multifidus muscle was positively correlated with the VAS, symptom duration, and ODI, respectively (r = 0.515, 0.614, and 0.548, P < 0.05). Sagittal plane balance, LL, PT, and the average degeneration degree of the multifidus were the risk factors for PI-LL mismatch (OR: 15.447, 95% CI: 1.274-187.269; OR: 0.001, 95% CI: 0.000-0.099; OR: 107.540, 95% CI: 5.195-2,225.975; OR: 52.531, 95% CI: 1.797-1,535.551, P < 0.05). Conclusion: The PVM on the concave side was larger than that on the convex side in ADS irrespective of whether PI-LL matched or not. PI-LL mismatch could aggravate this abnormal change, which is an important cause of pain and disability in ADS. Sagittal plane imbalance, decreased LL, higher PT, and larger average degeneration degree of the multifidus were independent risk factors for PI-LL mismatch.

Incidence and risk factors of lumbar plexus injury in patients undergoing oblique lumbar interbody fusion surgery.

PURPOSE: To investigate the incidence and risk factors of lumbar plexus injury (LPI) after oblique lumbar interbody fusion (OLIF) surgery. METHODS: A total of 110 patients who underwent OLIF surgery between January 2017 and January 2021 were retrospectively reviewed. Patients were divided into two groups: the group with LPI (LPI group) and the group without LPI (non-LPI group). The baseline demographic data, surgical variables and radiographic parameters were compared and analyzed between these two groups. RESULTS: Among all participants, 13 (8.5%) had LPI-related symptoms postoperatively (short-term), and 6 (5.5%) did not fully recover after one year (long-term). Statistically, there were no significant differences in the baseline demographic data, surgery duration, intraoperative blood loss, preoperative diagnosis, surgical procedures used and incision length. Compared with the non-LPI group, patients in the LPI group had a narrower OLIF channel space. In LPI group, the anterior edge of left psoas major muscle overpasses the anterior edge of surgical intervertebral disk (IVD) on axial MRI. Logistic regression analysis revealed that narrow OLIF channel space and the anterior edge of left psoas major muscle overpassing the anterior edge of surgical IVD on axial MRI were independently associated with both short-term and long-term LPI. CONCLUSION: Narrow OLIF channel space and the anterior edge of left psoas major muscle overpassing the anterior edge of surgical IVD are significant risk factors of OLIF surgery-related LPI. Surgeons should use preoperative imaging to adequately assess these risk factors to reduce the occurrence of LPI.

Modified Posterior Vertebral Column Resection for Patients with Thoracolumbar Kyphotic Deformity.

Old compression vertebrae fracture or congenital kyphoscoliosis with abnormal vertebral body development and other diseases that invade the spine may cause severe thoracolumbar kyphotic deformity, often accompanied by intractable low back pain or compression of the spinal cord, leading to severe neurological symptoms or even paralysis. If conservative treatment cannot relieve the symptoms or correct the deformities, surgical treatment is usually needed. For severe kyphotic deformity, reconstruction of the physiological curvature and rigid fixation determine the prognosis of the patients. Osteotomy and orthopedics are the standard procedure for deformities with severe compression of the front and middle column, but the trauma to the patients is high, with a long operation time and massive blood loss. To avoid these disadvantages, we have developed a modified technique to remove the diseased vertebra unilaterally. In this technique, we use a modified trephine to resect the vertebral columns like in the pedicle screw technique by adding a locking instrument that can restrict the trephine to lower the risk of osteotomy and shorten the surgery time and blood loss.

Comparisons between needle puncture and chondroitinase ABC to induce intervertebral disc degeneration in rabbits.

PURPOSE: This study aimed to compare the effect of needle puncture and chondroitinase ABC (ChABC) injection on inducing intervertebral disc (IVD) degeneration (IVDD) in rabbits. METHODS: Sixteen New Zealand white rabbits were used in this study. Briefly, the rabbits were divided into four groups. In the annulus fibrosis (AF) needle puncture group, a 16-G needle was used to puncture the L5-6 and L6-7 IVDs, while in the sham group, these IVDs were not punctured. In the ChABC group, 30 µL 0.5 Unit/mL ChABC was injected into L5-6 and L6-7 IVDs using a 26-G needle, while in the vehicle group, these IVDs were injected with 30 µL phosphate-buffered saline (PBS). X-ray and MRI scans were performed at the 4th, 12th and 16th weeks postoperatively. Histological, immunohistochemical and biochemical analyses were performed at the 16th week postoperatively. RESULTS: Both needle puncture and ChABC successfully established IVDD in rabbits at 4th, 12th and 16th weeks, confirmed by X-ray and MRI scan. The progression of IVDD went in a time-dependent manner. The IVDD in the ChABC group was less severe than in the needle puncture group throughout the study. Aggrecan and type II collagen significantly decreased, while tumor necrosis factor-α and superoxide dismutase 2 increased in the needle puncture and ChABC groups, compared with the sham and PBS groups. CONCLUSIONS: Both AF needle puncture and ChABC injection can successfully induce IVDD in rabbits. Compared with ChABC injection, AF needle puncture can induce more severe IVDD.

Antioxidant Effects of Resveratrol in Intervertebral Disk.

Intervertebral disk (IVD) degeneration (IVDD) can cause various spinal degenerative diseases. Cumulative evidence has indicated that IVDD can result from inflammation, apoptosis, autophagy, biomechanical changes and other factors. Currently, lack of conservative treatment for degenerative spinal diseases leads to an urgent demand for clinically applicable medication to ameliorate the progression of IVDD. Resveratrol (3,5,4'-trihydroxy-trans-stilbene), a polyphenol compound extracted from red wine or grapes, has shown protective effects on IVD, alleviating the progression of IVDD. Resveratrol has been demonstrated as a scavenger of free radicals both in vivo and in vitro. The antioxidant effects of resveratrol are likely attributed to its regulation on mitochondrial dysfunction or the elimination of reactive oxygen species. This review will summarize the mechanisms of the reactive oxygen species production and elaborate the mechanisms of resveratrol in retarding IVDD progression, providing a comprehensive understanding of the antioxidant effects of resveratrol in IVD.

Lumbar Disk Degeneration in Female Patients with and without Ovariectomy: A Case-Control Study.

OBJECTIVE: We sought to provide clinical evidence of the potential influence of ovariectomy (OVX) on intervertebral disk degeneration. METHODS: We retrospectively reviewed patients with a history of OVX who visited our hospital for lower back pain. In addition, 60 age-matched patients without OVX were randomly selected as control subjects. Next, the following demographic data were recorded and compared among groups: age, body mass index, duration of OVX, history of smoking, alcohol use, hypertension, diabetes, cardiocerebrovascular disease, hyperlipemia, osteoporosis, and degenerative spondylolisthesis. Next, the severity of lumbar disk degeneration, evaluated by the modified Pfirrmann grading system, was compared between groups. Data analyses were performed with SPSS 20.0. software. RESULTS: A total of 15 OVX (unilateral, n = 10; bilateral, n = 5) patients were included with a mean age of 62.40 ± 10.64. The average durations of OVX were 21.33 ± 9.24 years. There existed no remarkable intergroup differences in the demographic data (P > 0.05). Overall, the average Pfirrmann grading scores from L1/2 to L5/S1 presented as L1/2 < L2/3 < L3/4 ≤ L5/S1 ≤ L4/5, with no marked differences between groups (P > 0.05). Nevertheless, OVX groups displayed a relatively higher score at each level than non-OVX group. Moreover, the scores from L3/4 to L5/S1 were higher in the bilateral OVX group relative to the unilateral OVX group while they were equal at L1/2 and L2/3. CONCLUSIONS: Our findings demonstrated that OVX contributed to the progression of lumbar disk degeneration to some extent, but it appeared to be a long-term event.

17ß-Estradiol alleviates intervertebral disc degeneration by inhibiting NF-κB signal pathway.

AIM: To investigate the effect of 17ß-Estradiol (E2) on intervertebral disc degeneration (IVDD) and the related mechanism. MATERIALS AND METHODS: Immunohistochemistry was used to detect the expression of estrogen receptor ß (ERß) within intervertebral discs of humans and rats. After that, rat IVDD model was established by needle puncture and bilateral ovariectomy. Then, the serum E2 level was detected by enzyme linked immunosorbent assay, and the degree of IVDD was evaluated by X-ray, magnetic resonance imaging, hematoxylin and eosin staining, and Safranin O-Fast Green staining. Finally, we used immunohistochemistry and immunofluorescence staining to determine the effect of E2 on nuclear factor kappa-B (NF-κB) signal pathway both in vivo and in vitro. KEY FINDINGS: We identified that IVDD was associated with lower levels of ERß and ERß levels were inversely correlated with IVDD. The histological staining and radiological results showed that E2 supplement could alleviate IVDD progression. Additionally, immunohistochemistry staining demonstrated that E2 could inhibit nucleus pulposus cell (NPC) apoptosis, matrix metalloproteinases (MMPs) synthesis, and degradation of extracellular matrix (ECM) by inhibiting the activation of NF-κB signal pathway. Furthermore, immunofluorescence staining showed that the above effects of E2 on the NF-κB signal pathway could be blocked by the estrogen receptor antagonist ICI182780 in vitro. Finally, inhibition of NF-κB signal pathway by BAY11-7082 could reduce MMPs synthesis and ECM degradation of NPCs. SIGNIFICANCE: Collectively, these findings indicated that E2 could effectively ameliorate IVDD by inhibiting NPC apoptosis via inhibition of NF-κB signal pathway.

Locking stand-alone cage versus anterior plate construct in anterior cervical discectomy and fusion: a systematic review and meta-analysis based on randomized controlled trials.

PURPOSE: To evaluate the efficacy of locking stand-alone cage (LSC) compared with anterior plate construct (APC) in anterior cervical discectomy and fusion (ACDF). METHODS: A comprehensive literature search was carried out in PubMed, Embase, Web of Science, and Cochrane Library to screen randomized controlled trials (RCTs) that directly compared LSC with APC in ACDF. The Cochrane Collaboration's tool was used for assessment of study quality. Data were analyzed with the Review Manager 5.3 software. RESULTS: A total of seven RCTs were included. The results revealed no significant differences between LSC and APC in ACDF regarding the fusion rate, Japanese Orthopaedic Association score, visual analogue scale score, neck disability index score, hospital stay, subsidence rate, cervical lordosis, segmental Cobb angle, and disc height. However, LSC was associated with a significantly shorter operation time, less blood loss, lower overall incidence of dysphagia, and lower adjacent-level ossification (ALO) rate compared with APC. CONCLUSION: In summary, LSC is not only a safe and effective device for ACDF but also has the advantages of significantly reduced operation time, blood loss, overall incidence of dysphagia, and ALO rate over APC. Therefore, LSC is a better alternative than APC for the patients undergoing ACDF procedures.

Clinical Efficacy of Laminectomy with Instrumented Fixation in Treating Thoracolumbar Intradural Extramedullary Schwannomas: A Comparative Study.

BACKGROUND This study investigated the clinical effect of laminectomy plus pedicle screw fixation in treating thoracolumbar intradural extramedullary schwannomas. MATERIAL AND METHODS Between October 2011 and May 2017, 57 patients undergoing resection of thoracolumbar schwannomas were retrospectively identified and included in the study. Based on the surgical procedures used, all participants were assigned to either the laminectomy-only group (n=33) or the combination group (laminectomy plus pedicle screw fixation, n=24). All participants were followed up for over 2 years. In the laminectomy, the spinal process, vertebral laminae, and bilateral upper articular processes of the surgical segments were completely resected and the lower articular processes were reserved. For further analysis, we evaluated the pain levels using visual analogue scale (VAS) score. The assessment of neurological function was performed with Japanese Orthopaedic Association (JOA) score and Oswestry disability index (ODI). The comparisons of Cobb angle changes were carried out pre-surgery and post-surgery. RESULTS The demographic data were well matched between the laminectomy-only group and combination group, without significant differences (P>0.05). After surgery, both surgical procedures achieved significant improvement in VAS score, ODI, and JOA score (P<0.001), but no significant differences were found between these 2 surgical procedures (P>0.05). The postoperative change in Cobb angle indicated a significant difference in the laminectomy-only group, but not in the combination group (P<0.05). In addition, postoperative spinal instability/deformity was found in the laminectomy-only group (P<0.05). CONCLUSIONS In conclusion, the combination of laminectomy and pedicle screw fixation is a safe and effective surgical procedure when used to treat thoracolumbar schwannoma, and appears to be superior to the laminectomy-only procedure.

Oblique Lumbar Interbody Fusion with Stand-Alone Cages for the Treatment of Degenerative Lumbar Spondylolisthesis: A Retrospective Study with 1-Year Follow-Up.

Patients with degenerative lumbar spondylolisthesis (DLS) often suffer from years of low back pain (LBP) due to instability of the lumbar spine and the reduction of disc height. Since January 2016, we have performed oblique lateral interbody fusion (OLIF) on 154 patients. Among these, 56 patients who suffered from DLS underwent OLIF with stand-alone cages. Forty-two patients with a follow-up time that exceeded 1-year were enrolled for this study. The forty-two patients were followed up for at least one year. Operation segments ranged from L3-4 to L4-5. All the patients were with 1-level fusion. The mean postoperative ventral-disc height and dorsal-disc height increased significantly compared with preoperative (P < 0.05). A significant postoperative increase was also observed in the mean operative segmental lordotic angle and the whole lumbar lordotic angle (P < 0.05). Compared with preoperative, the postoperative VAS significantly decreased with no significant increase in the VAS in the last follow-up. The LBP was significantly relieved. The mean postoperative VAS of LBP decreased significantly compared with the preoperative ((1.6 ± 0.8) vs. (7.8 ± 0.8)). Postoperative complications included psoas major abscess and intervertebral space infection (1/56). Except for one patient whose cage subsided during the last follow-up, the other patients had good cage position. The one whose cage collapsed complained no symptoms including LBP. OLIF with stand-alone cages should be considered as a safe and effective option which can effectively alleviate LBP for the treatment of DLS.

Clinical Rehabilitation Effect of Postoperative Lower-Limb Training on the Patients Undergoing OLIF Surgery: A Retrospective Study.

Background: In this study, it was aimed to investigate the clinical rehabilitation effect of lower-limb training on the patients that undergo oblique lumbar interbody fusion (OLIF) procedures. Methods: The eligible participants undergoing OLIF procedures between 01/2017 and 07/2019 were identified. All the patients underwent one-segment fusion operation (L3-4 or L4-5). Based on whether the participants received postoperative rehabilitation training, they were divided into two groups: intervention group and control group. Postoperatively, the participants in the intervention group were trained with lower-extremity rehabilitation exercise and maintained for three months. All participants got reexamined at the first postoperative week, the second postoperative week, the first postoperative month, and the third postoperative month (last follow-up). Comparisons were made in terms of the lower-extremity muscle force, visual analogue scale (VAS) score, lumbar JOA score, Oswestry disability index (ODI), the incidence of deep venous thrombosis (DVT), and patient satisfaction. Results: Seventy-seven participants in the intervention group (32 males and 45 females) and 82 in the control group (39 males and 43 females) were incorporated in this study. The median age of the participants was 57 years (39∼73) in the intervention group and 54 years (35∼71) in the control group. No statistical significance between the two groups was found (P > 0.05). ODI score was less in the intervention group as compared to the control group in the first week after surgery (P=0.029). VAS and JOA scores were better in the intervention group in the first two weeks after surgery (P < 0.05). DVT incidence in the intervention group was lower than the control group at final follow-up (P=0.037). Both group participants have achieved good grading in muscle force rehabilitation but no significant differences between the two groups. Additionally, satisfaction was higher in the intervention group than the control group. Conclusions: In summary, postoperative lower-extremity rehabilitation exercise can effectively accelerate patients' health recovery from the OLIF surgery and increase their satisfaction.

Time-to-event analyses of lower-limb venous thromboembolism in aged patients undergoing lumbar spine surgery: a retrospective study of 1620 patients.

After spine surgery, venous thromboembolism (VTE) is not uncommon in aged patients. This study investigates time-to-event risk factors of postoperative VTE based on medical records of aged patients (age≥60 yr) between January 2013 and December 2018. All participants had undergone lower extremity ultrasonography pre- and postoperatively at the first, second, fourth, eighth, and twelfth weeks. Mann-Whitney U tests and chi-square tests were used for univariate analyses, and Cox regression was utilized for multivariate analyses. A total of 1620 cases were recruited, VTE group (N=382, 23.6%) and non-VTE group (N=1238, 76.4%), aged 67 (IQR 11) years and 65 (IQR 6) years, respectively. The univariate analyses indicated significant differences between the VTE and non-VTE groups regarding advanced age, VTE history, hypertension, fusion, hospital stay, FIB, HDL, D-dimer, and TC (all P<0.05). The Cox regression showed that advanced age (OR=1.108; 95% CI, 1.091-1.126), VTE history (OR=4.962; 95% CI, 3.849-6.397), and hypertension (OR=1.344; 95% CI, 1.084-1.667) were the risk factors for postoperative VTE (P<0.05). The time-to-event analyses indicated that the hazard of VTE formation was highest in the first postoperative week. In conclusion, advanced age, VTE history, and hypertension are main risks for VTE formation, particularly in the first postoperative week.