Tomographic, cadaveric and clinical study of safe corridors for insertion of implants in the thoracolumbar spine of dogs and cats using a lateral approach

OBJECTIVES

This study aimed to: describe a lateral vertebral corridor (T6-L7) for the implantation of screws and polymethylmethacrylate to treat thoracolumbar vertebral injuries; assess the feasibility and safety of this approach using computed tomography; assess the learning curve of this technique in canine cadavers; and assess the outcomes in injured dogs and cats in a retrospective clinical study.

MATERIALS AND METHODS

Tomographic study: Lateral vertebral corridors were defined using computed tomography images of normal canine spines in the transverse plane. Cadaveric study: Corridors were drilled by a novice neurosurgeon on the cadavers, and deviation from an angle of 90° was evaluated on computed tomography in chronological order to assess the learning curve.

CLINICAL STUDY

The medical records (from 2008 to 2022) of dogs and cats treated for thoracolumbar vertebral injury using the lateral approach were reviewed.

RESULTS

Computed tomography revealed that the lateral corridors were safe and effective. A progressive reduction in the deviation between the measured and ideal insertion angles was observed in the cadaveric part of the study. Overall, 17/30 animals (56.7%) regained the ability to walk without assistance postoperatively and 3/11 animals (27.3%) that had lost deep pain sensation. There were 3/30 (10%) minor complications and 8/30 (26.7%) major complications, including perioperative death and euthanasia.

CLINICAL SIGNIFICANCE

Lateral vertebral corridors with an orientation angle of 90° may be safely used in caudal thoracic and lumbar vertebrae (T6-L7) in a freehand technique to treat vertebral fractures and/or luxations in dogs and cats.

Application of a locking cortical pearl plate system to the feline lumbar vertebral column: a cadaveric study

AIMS

To assess the feasibility and safety of a locking cortical pearl plate system for the repair of lumbar vertebral fractures and luxation in cats using an ex vivo feline model.

METHODS

This cadaveric study of the lumbar vertebral column (L1-L7) involved 28 Domestic Short-hair cats without vertebral column pathology. Surrounding soft tissue was removed, except for the paravertebral musculature, joint capsules, and ligaments associated with the L1-L7 vertebrae. To determine whether the application of a 2.0-mm, 69-mm-long, 12-hole locking cortical pearl plate (LCPP) and screws was feasible, the dimensions of the feline lumbar vertebral bodies (length, width, and height) were measured using CT imaging. Width and height were evaluated at five locations along the length of the vertebrae with implant corridors (cor 1-cor4) located in between. Following CT, plates were applied to the vertebral columns. After implantation, another CT scan was performed to evaluate plate positions, screw trajectories, screw implantation angles, and vertebral canal breaching. Implantation was classified according to the modified Zdichavsky scoring system for vertebral canal penetration and grade I and IIa defined as acceptable.

RESULTS

A total of 371 screws were inserted into the lumbar vertebral bodies, and breaching occurred in 32 cases (8.6%), of which 29 (90.6%) were at L6 and L7. The median angle of inserted screws was 61.6° (min 53.4°, max 76.3°). Aside from one location, no significant angle deviations were observed between breaching (median 62.8°; min 53.4°, max 76.3°) and non-breaching (median 61.2°; min 53.8°, max 74.7°) screws. All 267 screws implanted in L1-L5 were graded I or IIa (acceptable). In contrast, low rates of acceptable implantation were achieved for L6 (52/60; 86.7%) and L7 (24/44; 54.4%), caused by clustering of breachings in corridor 3 of the two vertebrae.

CONCLUSIONS

Application of the LCPP immediately proximal to the transverse processes and ventral to the pedicles with a screw implantation angle of 60° is feasible and appears safe for L1-L5, resulting in a low number of vertebral canal breaches and a high rate of acceptable implantations.

CLINICAL RELEVANCE

The 2.0-mm, 69-mm-long, 12-hole LCPP can be considered an acceptable option for treating feline vertebral fractures and luxations of L1-L5. It cannot be recommended for use in corridor 3 of L6 or L7 due to the high risk of breaching the vertebral canal.

Assessment of the accuracy of patient-specific drilling guides for cervical (C5-C6) and lumbar (L4-L5) vertebrae in cats

Ten sets of vertebral biomodels and the corresponding drilling guides were created to evaluate the implantation accuracy in the cervical (C5-C6) and lumbar (L4-L5) vertebrae of cats. Smooth pins were implanted using the guides on the right side of five randomly assigned biomodel sets and on the left side of the remaining sets, with the contralateral side undergoing freehand implantation. Subsequently, a new tomographic study was conducted to measure the implantation angles. The pre-implantation angles were compared with the post-implantation angles between the techniques and among the sets. The guide-assisted implantation exhibited a lower dispersion compared to the freehand technique, with coefficients of variation of -1.95 and 48.9 in the cervical vertebrae and 1.98 and 9.39 in the lumbar vertebrae, respectively. However, no statistical difference was observed between the pre- and post-implantation angles, nor when comparing the vertebral segments (P > 0.05). Under the study conditions, the use of the guide failed to result in more accurate implantations in the C5-C6 and L4-L5 vertebral biomodels of cats.

Evaluation of Safe Insertion Angles for Spinal Needles and Safe Intensity of the Holmium:YAG Laser during Percutaneous Laser Disc Ablations in Feline Cadavers

In the context of veterinary medicine, minimally invasive techniques for feline spinal surgery remain underexplored, particularly for percutaneous laser disc ablation (PLDA) when using the Holmium:YAG (Ho:YAG) laser. This study aimed to refine the application of the Ho:YAG laser in PLDA by determining the optimal laser intensity and safe insertion angles for the thoracic and lumbar intervertebral discs (IVDs) in cats. Through utilizing computed tomography (CT) for precise guidance, this research involved a cadaveric study of 10 cats to evaluate the spatial configurations that allow for safe needle insertions and effective laser ablation. Various energy settings of the Ho:YAG laser (20 J, 40 J, and 60 J) were tested to ascertain the balance between adequate disc vaporization and minimal adjacent tissue damage. The results demonstrate that a 40 J setting is the most effective in achieving significant disc decompression without compromising surrounding tissue integrity. Additionally, the CT scans proved crucial in confirming the accuracy of the needle placement and the safety of the laser application angles. This study established that the 40 J setting on the Ho:YAG laser, combined with CT-guided insertion techniques, offers a reliable method for PLDA, thus enhancing the safety and efficacy of feline spinal surgeries.

Thoracic Vertebral Canal Stenosis and Vertebral Instability in a Young Minuet Cat

This report describes a unique case of thoracic vertebral canal stenosis and vertebral instability in a 1 yr old Minuet cat. The cat presented with a history of chronic progressive nonambulatory paraparesis. Myelography with neutral and stress positions revealed dynamic compression at T1-4. Computed tomography and MRI revealed multiple sites of vertebral endplate osteolysis, adjacent bone sclerosis, intervertebral disk space narrowing, and spondylotic bridging within the cervical and cranial thoracic vertebral bodies and pedicles, particularly at C6-T4. The cat underwent a right-sided T1-4 hemilaminectomy and C7-T4 vertebral stabilization using positively threaded profile pins and polymethylmethacrylate. The cat fully recovered without any complication. The case highlights the potential for young cats, especially those with a chondrodysplastic condition, to develop vertebral canal stenosis and vertebral instability. The surgical treatment described herein resulted in an excellent outcome.

Long-Term Follow-Up of Dogs and Cats after Stabilization of Thoracolumbar Instability Using 2-0 UniLock Implants

Traumatic vertebral fracture or luxation often results in spinal instability requiring surgical stabilization. This study describes the long-term outcome of spinal stabilization using a unilateral 5-hole 2-0 UniLock implant in eight dogs and two cats with trauma-induced thoracolumbar vertebral luxation/subluxation and presumed instability, as assessed by a combination of preoperative radiographs and MRI using a 3-compartment method. The UniLock plate was secured with four monocortical locking screws in adjacent vertebral bodies. Additional pins and facet screws were used in several patients. Postoperative radiographs and MRI studies showed restoration of the main spinal axis in all patients and satisfactory implantation of the screws in the vertebral bodies, with no intrusion in the vertebral canal or in the adjacent intervertebral disc spaces. Neurological status improved in nine patients six weeks postoperatively. Partial implant failure was detected in three patients with no long-term consequences. After 12 months, seven patients reached full recovery with no neurological deficit, two patients were euthanized (including one owing to an unrelated condition), and one remained paraparetic. The results of this study demonstrate that using a 2-0 UniLock implant to stabilize the thoracolumbar spine results in satisfactory long-term recovery in most dogs and cats with traumatic spinal luxation/subluxation and presumed instability. Complications may occur but do not require revision surgery and do not affect clinical outcomes.

Biomechanical comparison of ex vivo lumbar vertebral fracture luxations stabilized with tension band or polymethylmethacrylate in cats

OBJECTIVE

To evaluate spinal stabilization with tension band stabilization (TS) in cats compared to screw and polymethylmethacrylate fixation (SP).

STUDY DESIGN

Ex vivo study.

SAMPLE POPULATION

Sixteen feline thoracolumbar spinal specimens.

METHODS

The intact specimens were mounted in a six-degree-of-freedom biaxial testing machine for nondestructive testing to obtain the neutral zones (NZ) and range of motion (ROM) in flexion and extension. Thereafter, nondestructive testing was consecutively performed after destabilization by disc fenestration and partial L1 corpectomy and after treatment with either TS or SP. Load to failure was compared after surgical treatment in flexion. Significance was assessed by Student's t test or Wilcoxon signed-rank test.

RESULTS

Range of motion was 26.4° ± 2.2° in TS constructs and 13.4° ± 2.1° in SP constructs (P = .0005). When flexion and extension were analyzed separately, no difference was found for ROM in flexion (SP, 7.0° ± 3.7°; TS, 8.3° ± 2.1°; P = .38). In extension, the mean displacement was 6.4° ± 2.7° and 18.1° ± 5.1° in SP and TS constructs, respectively (P = .0001). Neutral zone was 2.9° ± 0.6° and 7.5° ± 0.8° for the SP and TS groups, respectively (P = .0003). Screw and polymethylmethacrylate fixation constructs were two times stiffer (P = .045).

CONCLUSION

Tension band stabilization provided stability comparable to SP in flexion. In extension, ROM of SP constructs was half that of TS constructs. The mode of failure of TS was related to the limited dorsal bone stock of feline lumbar vertebrae.

CLINICAL SIGNIFICANCE

Surgeons should be aware of the limited stability in extension provided by TS when it is used to stabilize thoracolumbar spinal injuries. Our results provide evidence to justify additional studies to clarify the type of fractures amenable to TS.

Clinical reasoning in feline spinal disease: which combination of clinical information is useful?

OBJECTIVES

The aim of this study was to evaluate if a combination of discrete clinical characteristics can be used to identify the most likely differential diagnoses in cats with spinal disease.

METHODS

Two hundred and twenty-one cats referred for further evaluation of spinal disease were included and categorised as follows: non-lymphoid neoplasia (n = 44); intervertebral disc disease (n = 42); fracture/luxation (n = 34); ischaemic myelopathy (n = 22); feline infectious peritonitis virus myelitis (n = 18); lymphoma (n = 16); thoracic vertebral canal stenosis (n = 11); acute non-compressive nucleus pulposus extrusion (n = 11); traumatic spinal cord contusion (n = 8); spinal arachnoid diverticula (n = 7); lumbosacral stenosis (n = 5); and spinal empyema (n = 3). Information retrieved from the medical records included signalment, clinical history and clinical presentation. Univariate analyses of variables (clinical history, breed, age, sex, general physical examination findings, onset, progression, spinal hyperaesthesia, asymmetry, ambulatory status and neuroanatomical location) were performed, and variables were retained in a multivariate logistic regression model if P <0.05.

RESULTS

Multivariate logistic regression revealed that intervertebral disc disease most often occurred in middle-aged, purebred cats with a normal general physical examination and an acute onset of painful and progressive clinical signs. Ischaemic myelopathy occurred most often in older cats with a stable or improving, non-painful, lateralising, C6-T2 myelopathy. Spinal fracture/luxation occurred most often in younger cats and resulted most often in a peracute onset, painful, non-ambulatory neurological status. Concurrent systemic abnormalities or abnormal findings detected on general physical examination were significantly associated with feline infectious peritonitis virus myelitis, spinal lymphoma or spinal empyema.

CONCLUSIONS AND RELEVANCE

This study suggests that using easily identifiable characteristics from the history and clinical examination can assist in obtaining a preliminary differential diagnosis when evaluating cats with spinal disease. This information could aid veterinary practitioners in clinical decision-making.

Computed tomographic study of safe implantation corridors in rabbit lumbar vertebrae

OBJECTIVES

A study was performed to evaluate the lumbar vertebrae of domestic rabbits using computed tomography (CT) in order to identify safe corridors for implant insertion.

METHODS

Computed tomography imaging of 20 adult New Zealand white rabbits was evaluated using three-dimensional multiplanar reconstruction, and safe corridors were determined. Following corridor determination, implant placement was performed, and imaging was repeated.

RESULTS

The cranial and caudal endplates contained the majority of the vertebral bone stock, and were an average of 3.14 and 3.30 mm in length, respectively. The mean safe corridor angle was 62.9 degrees (range: 58.8-66.7), and the mean width of the corridor was 2.03 mm (range: 1.60- 2.07). Post-placement imaging revealed that 35% of the pins demonstrated errors of placement, most commonly canal impingement.

CONCLUSIONS

The results of the corridor evaluation indicate that an insertion angle of approximately 60 degrees relative to the sagittal midline is appropriate for implant insertion in the lumbar vertebrae of New Zealand white rabbits. Additionally, due to the hourglass shape of rabbit vertebrae, the endplates provide maximal bone stock for implant purchase, so insertion should be attempted in these regions. However, the high percentage of errors in placement indicate the need to more clearly define entry points to access the canal, and highlight the challenges of appropriate placement in the small bones of rabbits.