Early Postoperative Loss of Disc Height Following Transforaminal and Lateral Lumbar Interbody Fusion: A Radiographic Analysis.

STUDY DESIGN: Retrospective comparative radiological study. PURPOSE: To analyze the difference in early disc height loss following transforaminal and lateral lumbar interbody fusion (TLIF and LLIF). OVERVIEW OF LITERATURE: Minimal disc height loss facilitated by the polyaxial screw heads can occur naturally due to mechanical loading following lumbar fusion procedures. This loss does not usually cause any significant foraminal narrowing. However, when there is concomitant cage subsidence, symptomatic foraminal compromise could occur, especially when posterior decompression is not performed. It is not known whether the type of procedure, TLIF or LLIF, could influence this phenomenon. METHODS: Retrospectively, patients who underwent TLIF and LLIF for various degenerative conditions were shortlisted. Each of their fused levels with the cage in situ was analyzed independently, and the preoperative, postoperative, and follow-up disc height measurements were compared between the groups. In addition, the total disc height loss since surgery was calculated at final follow-up and was compared between the groups. RESULTS: Forty-six patients (age, 64.1±8.9 years) with 70 cage levels, 35 in each group, were selected. Age, sex, construct length, preoperative disc height, cage height, and immediate postoperative disc height were similar between the groups. By 3 months, disc height of the TLIF group was significantly less and continued to decrease over time, unlike in the LLIF group. By 1 year, the TLIF group demonstrated greater disc height loss (2.30±1.3 mm) than the LLIF group (0.89±1.1 mm). However, none of the patients in either group had any symptomatic complications throughout follow-up. CONCLUSIONS: Although our study highlights the biomechanical advantage of LLIF over TLIF in maintaining disc height, none of the patients in our cohort had symptomatic complications or implant-related failures. Hence, TLIF, as it incorporates posterior decompression, remains a safe and reliable technique despite the potential for greater disc height loss.

Migration and Spontaneous Extrusion of a Lumbar Spinal Fusion Rod From the Gluteal Region.

Instrumented fusion with rods and pedicle screws is often performed for the surgical treatment of adult spinal deformity (ASD). One of the complications of such long construct fusions is that of pseudoarthrosis, which can present with implant loosening, failure, and rod breakage. However, migration and spontaneous extrusion of the rod is relatively rare and has yet to be reported in the literature. We report a gentleman with previous long construct instrumented fusion done six years ago for ASD, who presented with gluteal pain. Radiographs revealed rod breakage and caudal migration towards the left gluteal region. He subsequently reported spontaneous extrusion of the broken rod through the gluteal skin, without the need for surgical removal. This case is reported for its rarity and to raise awareness about the rare occurrence of rod migration after breakage that can lead to potential complications if left unattended.

Morphological Parameters of the Thoracic Pedicle in an Asian Population: A Magnetic Resonance Imaging-Based Study of 3324 Pedicles.

STUDY DESIGN: A cross-sectional magnetic resonance imaging (MRI)-based anatomical study. OBJECTIVES: Instrumentation of the thoracic spine may be challenging due to the unique pedicle morphology and the proximity of vital structures. As prior morphological studies have mostly been done in Caucasians, our study aims to determine the optimal pedicle screw size for transpedicular fixation in an Asian population. METHODS: A retrospective analysis of 400 patients who had undergone MRI of the thoracic spine was performed. A total of 3324 pedicles were included. Pedicle morphology was graded qualitatively based on the size of its cancellous channel, and quantitatively with the following parameters: pedicle transverse diameter, pedicle screw path length, and pedicle angle. Subgroup analysis based on gender was performed. RESULTS: Mean pedicle transverse diameter was the narrowest at the T4 (2.9 ± 1 mm) and T5 (3.1 ± 1.1 mm) level. The mean pedicle screw path length progressively increased from T1 (34 ± 4.6 mm) to T12 (47 ± 4.6 mm). The mean pedicle angle was the largest at T1 (34° ± 7.9°) and decreased caudally, to 9.4° ± 3.8° at the T12 level. Females had significantly lower mean pedicle diameter and screw path length than males at every vertebral level; however, they had a larger pedicle angle at T8 to T10. The most common size of the pedicle cancellous channel was more than 4 mm. CONCLUSION: Morphological differences in the Asian pedicle suggest that caution needs to be taken during thoracic spine instrumentation, particularly in Asian females who have significantly smaller pedicles. In such cases, the use of alternative techniques or intraoperative navigation may be useful.

Reliability of the new modified Moro's classification and oblique corridor grading to assess the feasibility of oblique lumbar interbody fusion.

INTRODUCTION: The modified Moro's classification (MMC) of psoas morphology and oblique corridor (OC) grading were recently proposed. Their reliability needs to be tested. METHODS: T2 weighted lumbar disc level axial-cut MRI images of patients with degenerative spondylosis were distributed to five spine surgeons. The inter and intra-rater reliability of MMC and OC grading were calculated based on their ratings. RESULTS: Based on kappa statistics, we inferred that both MMC and OC grading are reliable measures. CONCLUSION: Both MMC and OC grading, in combination, can be used to predict the feasibility of oblique lumbar interbody fusion and aid in patient selection.

Factors Influencing Early Disc Height Loss Following Lateral Lumbar Interbody Fusion.

STUDY DESIGN: Retrospective radiological analysis. PURPOSE: To analyze the factors influencing early disc height loss following lateral lumbar interbody fusion (LLIF). OVERVIEW OF LITERATURE: Postoperative disc height loss can occur naturally as a result of mechanical loading. This phenomenon is enabled by the yielding of the polyaxial screw heads and settling of the cage to the endplates. When coupled with cage subsidence, there can be significant reduction in the foraminal space which ultimately compromises the indirect decompression achieved by LLIF. METHODS: Seventy-two cage levels in 37 patients aged 62±10.2 years who underwent single or multilevel LLIF for degenerative spinal conditions were selected. Their preoperative and postoperative follow-up radiographs were used to measure the anterior disc height (ADH), posterior disc height (PDH), mean disc height (MDH), disc space angle (DSA), and segmental angle. Correlations between the loss of disc height and several factors, including age, construct length, preoperative lordosis, postoperative lordosis, disc height, cage dimensions, and cage position, were analyzed. RESULTS: We found that the lateral interbody cages significantly increased ADH, PDH, MDH, and DSA after surgery (p<0.0001). However, there was a loss of disc height over time. All postoperative disc height parameters, especially the amount of increase in MDH (r=0.413, p<0.0001) after surgery, showed a significant positive association with early disc height loss. The levels demonstrating a significant (≥25%) height loss were those that exhibited a substantial height increase (128.3%, 4.6±3.0 to 10.5±5.6 mm) postoperatively. However, the levels that showed less than 25% height loss were those that exhibited, on average, only a 57.4% height increase post-operatively. CONCLUSIONS: The greater the postoperative increase in disc height, the greater the disc height loss throughout early follow-up. Therefore, achieving an optimal disc height rather than overcorrection is an important surgical strategy to adopt when performing LLIF.

Spinal Navigation during Orthopedic Residency Training: A Double-Edged Sword?

BACKGROUND: Orthopedic residents in our institute have the opportunity to participate in navigation-assisted spine surgery during their residency training. This paves the way for a new dimension of learning spine surgery, which the previous generation was not exposed to. To study this in detail, we conducted a cross-sectional descriptive survey among our residents to analyse their perception, understanding, and competency regarding pedicle screw application using spinal navigation. METHODS: We selected orthopedic residents (n = 20) who had completed 3 years of training that included at least one rotation (4-6 months) in our spine division. They were asked to respond to a four-part questionnaire that included general and Likert scale-based questions. The first two parts dealt with various parameters regarding spinal navigation and free-hand technique for applying pedicle screws. The third part dealt with residents' opinion regarding the advantages and disadvantages of spinal navigation. The final part was an objective analysis of residents' ability to identify the pedicle screw entry points in selected segments. RESULTS: We found that our residents were better trained to apply pedicle screws using spinal navigation. The mean Likert scale score for perception regarding their competency to apply pedicle screws using spinal navigation was 3.65 ± 0.81, compared to only 2.8 ± 0.77 when using the free-hand technique. All residents agreed that spinal navigation is an excellent teaching tool with higher accuracy and greater utility in anatomically critical cases. However, 35% of the residents were not able to identify the entry points correctly in the given segments. CONCLUSIONS: All selected residents were perceived to be competent to apply pedicle screws using spinal navigation. However, some of them were not able to identify the entry points correctly, probably due to overreliance on spinal navigation. Therefore, we encourage residents to concentrate on surface anatomy and tactile feedback rather than completely relying on the navigation display monitor during every screw placement. In addition, incorporating cadaveric and saw bone workshops as a part of teaching program can enhance better understanding of surgical anatomy.

Bisphosphonate-associated peri-implant fractures: a new clinical entity? A series of 10 patients with 11 fractures.

BACKGROUND AND PURPOSE: The current definition of atypical femoral fractures (AFFs) associated with bisphosphonate use includes only de novo fractures. However, in recent years reports of bisphosphonate-associated periprosthetic fractures involving stemmed arthroplasty implants have emerged. In a case series of peri-implant fractures in femurs with plate/screw constructs, we aimed to assess similarities with classical AFFs and how their location may have implications for the pathogenesis and management of AFFs. PATIENTS AND METHODS: We retrospectively identified 10 patients with 11 peri-implant fractures. RESULTS: The patients were ambulant women, mean age 80 (70-92) years. Mean duration of bisphosphonate use was 5 (1-10) years. The peri-implant fractures were sustained an average of 4 years (6 months to 9 years) from the time of index surgery. They were all associated with low-energy mechanisms. 8 fractures occurred near the tip of a plate, while 3 traversed the penultimate screwhole of a plate. The peri-implant fractures showed clinical and radiological features of atypicality such as lateral cortical thickening, simple fracture pattern, and lack of comminution. The patients underwent revision surgery, with bone grafting used in all but 1 case. Radiological union was evident after 2-4 months. INTERPRETATION: Atypical peri-implant fractures of the femur associated with bisphosphonate use may be a new entity. Stress lesions and atypical fractures may tend to develop over stress risers along the operated femur. This finding has implications for the pathogenesis and clinical management of AFFs.

Mechanical failure of the distal radius volar locking plate.

PURPOSE: To review 9 cases of mechanical failure of the volar locking plate for distal radial fractures. METHODS: Records of 374 consecutive patients who underwent volar locking plating for distal radial fractures were reviewed. Mechanical failures of the volar locking plate were defined as plate breakage or bending, screw breakage or loosening, or collapse of articular fragments resulting in intra-articular screw extrusion. RESULTS: Nine mechanical failures occurred between 2 weeks and 3 months in 8 (2.4%) of the patients aged 25 to 82 (median, 74) years with AO fracture types of A3 (n=4), C1 (n=1), C2 (n=1), and C3 (n=3). Mechanical failures included screw pullout (n=5), locking plate bending (n=2), locking screws breakage (n=1), and loosening of locked variable angle screws (n=1). One patient underwent revision of fixation and 2 underwent implant removal. The remainder were treated conservatively. All patients were followed up for a minimum of 12 months; their mean flexion arc was 87 degrees (standard deviation [SD], 17) and the mean rotation arc was 136 degrees (SD, 29 degrees). According to the Green and O'Brien score, their outcomes were good (n=1), fair (n=4), and poor (n=3). CONCLUSION: Although mechanical failure of volar locking plate is uncommon, some are potentially preventable.