Assessment of Pedicle screw-Rod implantation as an external fixation method for tibial osteotomy in a canine model

Highlights

• •The pedicle screw-Rod configuration is an effective method for tibial fixation.
• •The pedicle screw-Rod configuration offers minimally invasive bone fixation.
• •The pedicle screw-rod configuration for tibial fixation has minimal complications.
• •The use of a pedicle screw-rod configuration improved tibial osteotomy union.
• •Pedicle screw-Rod fixation in the tibia enabled a swift return of limb function.

Abstract

Recent advancements in minimally invasive osteosynthesis have improved atraumatic techniques for bone fracture fixation. Pedicle screws are implants primarily used for the internal fixation of the spine. To our knowledge, no studies have assessed the use of Pedicle screw-Rod for fixing long bone fractures or osteotomies. Our study aimed to assess the efficiency and performance of this implant as an external fixation method for experimentally induced tibial fractures, offering a novel surgical approach to tibial fixation. With approval from the Institutional Animal Care Committee, eight healthy, intact male dogs weighing 20–22 kg and aged 10–12 months of mixed breeds underwent aseptic surgical fixation of tibial osteotomies with Pedicle screw-Rod configuration using a minimally invasive medial approach to the tibia. All dogs were placed in the single treatment group. Postoperative clinical and radiographic evaluations were performed. The fixation device functioned effectively until removal. Lameness was fully resolved in all animals by 21 days post-operation. Clinical union occurred at 5.80 ± 1.30 weeks, while complete bone union was achieved at 11.40 ± 1.51 weeks after surgery. Postoperative mechanical medial proximal and distal tibial angles were, 92.00° (92.00°, 91.50°) and 93.40° ± 1.14°, respectively. The tibial valgus was 5.20° ± 1.48°, and tibial plateau angles measured 22.00° (23.00°, 22.00°). There were no significant differences noted when comparing values before and after the operation. Postoperative rotational alignment was anatomical, with satisfactory bone apposition. The study found that using a Pedicle Screw-Rod configuration for non-articular tibial osteotomy fixation is effective without significant complications.

Graphical abstract

1. Introduction

The tibia is a long bone that is essential for the motor functions of dogs and cats (Johnston & Tobias, 2017). Fractures of the tibia are frequently seen in dogs and cats, representing 10 to 20% of all fractures (Unger et al., 1990). Tibial fractures constitutes 21% of long bone fractures and 11.7% of appendicular fractures (Johnson et al., 1994). The most common type of tibial fracture is the diaphyseal fracture (Boone et al., 1986). Approximately 10 to 20% of tibial fractures are classified as open fractures, with the distal region of the tibia being the most common site for open fractures in adult animals (Boone et al., 1986).

Different techniques are available for the fixation of tibial fractures and the selection of the appropriate method is influenced by factors such as fracture location and its type, extent of soft tissue damage, infection, patient age, economic considerations, and the surgeon's preference (Johnston & Tobias, 2017). In recent years, there have been significant advancements in atraumatic techniques, now known as minimally invasive osteosynthesis (MIO) (Hudson et al., 2009). This technique encompasses various surgical approaches for bridging osteosynthesis, emphasizing minimal surgical intervention away from the fracture site and indirect fracture reduction techniques, such as percutaneous K-wiring, closed intramedullary nailing, and minimally invasive plate osteosynthesis (MIPO) (Guiot & Déjardin, 2011; Pozzi & Lewis, 2009; Schmökel et al., 2007). The success of the MIO technique lies in preserving the primary fracture hematoma and ensuring adequate blood supply at the fracture site (Farouk et al., 1998). Experimental research has demonstrated the critical role of maintaining the primary fracture hematoma and local blood circulation in enhancing callus formation and facilitating callus remodeling (Tsunoda et al., 1993). Over 18% of tibial fractures treated with open reduction and internal fixation (ORIF) necessitate reoperation due to a range of complications (Dudley et al., 1997). Certain complications are primarily linked to disturbances in the fracture hematoma and surrounding soft tissues, leading to interference and delays in bone healing (Tsunoda et al., 1993). The advantages of the MIO technique vary depending on the location of the fracture site. For bones like the tibia and radius, which have minimal soft tissue surrounding them, the MIO technique offers benefits by preserving the adjacent soft tissue (Pozzi et al., 2021).

Pedicle screws (PS) are implants used primarily for the internal fixation of the spine to correct deformities and stabilize it until a solid fusion is achieved (Boos & Webb, 1997). The use of PS in spinal fixation originated in Europe, with Raymond Roy-Camille pioneering their application through vertebral pedicles in 1970 (Roy-Camille et al., 1970). In the United States, Harrington was the first to utilize PS for reducing and fixing high-grade spondylolisthesis (Harrington, 1969). In 1982, Magerl introduced the initial technique for percutaneous PS insertion to provide external fixation of the spine (Magerl, 1982). By 1995, Matthews and Long presented a fully percutaneous Pedicle screw system (PPS) (Mathews & Long, 1995). Through advancements in screw design and the evolution of fixation devices, the PPS system is now employed in minimally invasive surgery (MIS) for spinal fixation across a broad range of spinal segments, from the thorax to the pelvis. This approach is utilized for various conditions, such as vertebral fractures, scoliosis, metastases, osteoporotic vertebral fractures, and discitis/pyogenic spondylosis (Anand et al., 2008; Deininger et al., 2009; Eck, 2011; Hikata et al., 2017; Ishii, 2012; Ishii et al., 2022; Tomycz et al., 2015). Biomechanical research on PS has examined their strength across various bone densities, focusing primarily on design and thread shape under different mechanical forces. The findings indicate that PS can withstand maximum forces regardless of bone density (Kim et al., 2012).

Providing a fixation method that is minimally invasive yet strong enough to allow early and pain-free movement of the limb is essential for the veterinary orthopedic surgeon. This approach not only aids in bone healing but also preserves the integrity of nearby soft tissues, simplifying patient care (DeCamp, 2015). To our knowledge, no studies have been conducted on the use of Pedicle screw-Rod (PS-R) fixation for fractures or osteotomies of long bones. Our study aimed to assess the efficiency and performance of this implant as an external fixation for experimentally induced tibial fractures, focusing on patient function, bone healing, alignment, and implant integrity, thereby introducing a novel surgical approach for bone fixation.

2. Methods

2.1. Ethics statement

Dogs were utilized for research purposes, with informed consent obtained and the animal shelter director fully informed. This study was reviewed and approved by the Animal Ethics Committee at the Urmia Veterinary Faculty (Urmia, Iran; Veterinary Faculty, Ref: IR-UU-AEC-3/79).

2.2. Animals

This study involved the utilization of eight healthy, intact male dogs (n = 8), aged between 10 and 12 months (10.75 ± 0.88), of mixed-breeds, weighing between 20 and 22 kg (20.81 ± 0.79). Due to the unavailability of dogs of the specific breed sought, mixed breed native dogs were employed. To minimize the impact of bone structure on the outcomes, standardization was conducted regarding bone length, cortical bone thickness, and body condition score relative to musculature bulk in the hind limb. Each dog was housed in an individual kennel maintained under suitable sanitary conditions and fed the same commercial diet. Prior to the study, all dogs underwent clinical and paraclinical assessments, including CBC, total protein (TP), and biochemical tests, to rule out any concomitant diseases. Subsequently, the selected dogs received deworming and vaccinations at least 30 days before the commencement of the research. After completion of the study and verification of complete bone fusion at the osteotomy site through radiology, ensuring the absence of complications and the restoration of normal function in all patients, all animals involved in this research were sterilized and either returned to the shelter or adopted through donation. This study explored the potential effectiveness of the PS-R configuration as a stable, rigid, and minimally invasive fixation device for tibial osteotomy. Given our objective to introduce a novel surgical approach for long bone fracture fixation, all animals in the study were grouped together to assess the efficacy and stability of utilizing PS-R configuration as external fixation for tibial osteotomy throughout the healing process.

2.3. Anesthesia procedures

In all studied animals, a blend of 0.01 mg/kg, Acepromazine maleate 1% (Alfasan, Woerden, Netherland) and 0.2 mg/kg Midazolam (Rotexmedica, Trittau, Germany) was administered intramuscularly for premedication. To induce anesthesia, a combination of 4 mg/kg Propofol (Propofol-Lipuro 1%, B. Braun, Melsungen AG, Germany) and 0.2 mg/kg Midazolam was employed. Anesthesia was continued using Isoflurane (Baxter Healthcare Corporation, Deerfield, USA) in Oxygen through a semi-closed circuit with a tracheal tube. Cefazolin (Tum Ekip pharmaceuticals, Istanbul, Turkey) was administered intravenously at a dosage of 22 mg/kg during anesthesia induction and subsequently repeated every 90 min throughout the procedure to prevent infections.

2.4. Surgical procedure

All surgical procedures were performed under aseptic conditions by the same surgeons. Following standard surgical preparation, a two-centimeter incision was made on the medial aspect of the right tibia, mid-shaft. The subcutaneous tissue and periosteum were dissected to expose the tibial diaphysis. A complete transverse osteotomy was performed at the mid-shaft of the tibia and fibula in all dogs using a sagittal blade (Stryker, Kalamazoo, USA), based on previous studies of tibial osteotomy in canine models (Bleedorn et al., 2014; Inoue et al., 2002). The fixation of the tibial osteotomy was unilaterally carried out from the medial aspect of the bone. For the insertion of monoaxial Pedicle screws, a stab incision was made on the skin, followed by dissection of the soft tissue to expose diaphysis of the bone. Pre-drilling was performed perpendicular to the longitudinal axis of the tibial diaphysis using a 3.2 mm drill bit (70% of the outer diameter of the screw) and an orthopedic drill (Stryker, Kalamazoo, USA). All fixations were carried out using four 4.5 mm, titanium monoaxial Pedicle screws (Atra Orthoped, Urmia, Iran) and a 6 mm, titanium Rod (Atra Orthoped, Urmia, Iran). Initially, two PS were positioned at a distance from the osteotomy gap to help maintain the bone axis, while the remaining two were placed near the gap to minimize stress at the bone-screw interface (Fig. 1, A). All screws were aligned parallel to each other and perpendicular to the longitudinal axis of the bone in the same plane. Following precise realignment along the frontal and sagittal planes and the insertion of a 1.0 mm metal spacer in the osteotomy gap, a 6.0 mm titanium Rod was inserted through the Pedicle screw heads. The PS-R configuration was tightened with specialized nuts (Atra Orthoped, Urmia, Iran) designed for pedicle screws (Fig. 1, B). For proper and effective implantation, the longitudinal axis of the screw should be perpendicular to the longitudinal axis of the bone in the sagittal plane, and it is also ideal for the screws to be perfectly parallel to each other in the same plane (Fig. 1, C). Paying attention to this aspect will result in the creation of a more appropriate support surface for the Rod when placed in the heads of the screws, leading to increased strength. Additionally, it reduces the necessity to contour the Rod on the axial surfaces. Nevertheless, if the screws are not placed in the same plane, contouring of the Rod can be effective in neutralizing inappropriate forces to improve and maintain the alignment of bone segments, achieve anatomical reduction and, remove abnormal angles during the implantation and healing period (Fig. 1, D). Throughout the osteotomy and screw insertion process, the surgical site was continuously irrigated with copious sterile saline solution to prevent bone damage from heat. To maintain a 1.0 mm gap during fixation, a temporary 1.0 mm thick plate was inserted into the osteotomy gap. Closure of the soft tissue was performed using synthetic absorbable sutures (Dexon., Covidien, Mansfield, USA) and Nylon (Ethicon Inc., Somerville, USA) for the skin, employing continuous and interrupted patterns, respectively. Immediately after the surgery, the primary bandage was applied under aseptic conditions. After recovery from anesthesia, each dog was individually transferred to private kennels, each with an area of four square meters, for the duration of the recovery period.

Fig. 1.

Intraoperative photographs (A-D). After creating a transverse osteotomy using a sagittal blade at the midshaft of the tibia (black arrow), monoaxial Pedicle screws were subsequently placed unilaterally on the medial aspect of the bone (A). Following precise realignment along the frontal and sagittal planes, a 1.0 mm metal spacer was inserted in the osteotomy gap, and a 6.0 mm titanium rod was placed through the Pedicle screw heads. The PS-R configuration was tightened using specialized nuts designed for pedicle screws (B). For proper and effective implantation of the PS-R configuration, the longitudinal axis of the screws should align perpendicularly to the longitudinal axis of the bone in the sagittal view. Whenever feasible, it is advisable to position all screws in the same plane. By emphasizing this factor, a more suitable support surface for the rod at the screw head can be achieved, enhancing strength and counteracting improper forces (C). However, when the screws are not placed in the same plane, contouring the rod during implantation can effectively neutralize improper forces, improving bone segment alignment, facilitating anatomical bone reduction, and correcting abnormal angles (D).

2.5. Postoperative care

Bandages over the incision and around the screws were replaced daily for two consecutive weeks after surgery. After that, the bandages were replaced twice a week until the removal of the implant. The dogs were initially confined to cage rest for five days following the operation. After this period, they were permitted to leave the kennel, twice daily for controlled leash walks and exposure to sunlight. Postoperative pain management was carried out using tramadol hydrochloride (Aburaihan ‌Pharmaceutical Co, Tehran, Iran) at a dose of 4 mg/kg every eight hours and meloxicam (Metacam, Boehringer Ingelheim Vetmedica, USA) at a dose of 0.2 mg/kg once daily, orally, for five days. Cefazolin at a dose of 22 mg/kg, every 12 h was administered intravenously for five days to prevent infection. The fixation implant (PS-R) was retained until radiological union was established.

2.6. Clinical evaluation

Postoperative clinical evaluations (patient function) were performed in terms of weight bearing, degree of lameness and its duration, and the occurrence of any complications, including any signs of surgical site infection (SSI), erythema, sinus tracts at the location of the screws, and self-mutilation during the recovery period. To assess the quality of ambulation and limb support, the modified lameness grading score system was used (Table 1) (Vasseur et al., 1995). The evaluation was conducted every 48 h by only one person until normal ambulation and pain-free weight bearing were achieved.

Table 1.

Lameness grading score system, used to monitor dogs that underwent Pedicle screw-Rod for the fixation of tibial osteotomy (Vasseur et al., 1995).

category	score	Clinical sign
Walk and trot	1	No lameness noted at walk and trot
	2	No lameness at a walk and mild lameness at a trot
	3	Mild lameness at a walk and significant lameness at a trot
	4	Significant lameness at a walk and non-weight bearing at a trot
	5	Non weight bearing at a walk and trot
Standing	1	Normal weight bearing at a stance at a stance
	2	Mild decrease in weight bearing at a stance
	3	Significant decrease in weight bearing at a stance
	4	Occasional toe touching at a stance
	5	Hold limb of the ground at a stance
Contralateral limb	1	Readily accepts contralateral limb being held up and bears full weight on affected limb
	2	Offers resistance to elevation of contralateral limb but bears full weight on affected limb for more than 1 min after contralateral limb is elevated
	3	Offers moderate resistance to elevation of contralateral limb and replaces it after 30 s
	4	Offers resistance to elevation of contralateral limb and replaces it after 10 s
	5	Refuses to raise contralateral limb
Pain on the palpation	1	No signs of pain during palpation of affected limb
	2	Signs of mild pain during palpation of affected limb; dog turns head in recognition
	3	Signs of moderate pain during palpation of affected limb; dog pulls limb away
	4	Signs of severe pain during palpation of affected limb; dog vocalizes or becomes aggressive
	5	Dog will not allow examiner to palpate affected limb

2.7. Radiographic evaluations

Before surgery, two standard radiographic views (mediolateral and caudocranial) were taken for each dog. Additional radiographs were captured immediately post-operation and weekly until complete bone union was evident. All radiographs were taken with the same settings by a single operator without sedatives. Critical radiographic evaluation of bone alignment, fragment apposition, implant position and integrity, bone healing, and any complications was conducted by a specialized radiologist in a blinded fashion.

2.7.1. Bone healing

To assess radiographic union progress, a grading scale ranging from 1 to 5 was employed, focusing on callus formation, fracture line visibility, and the stage of union development (Table 2) (Whelan et al., 2002). In addition to monitoring radiographic union, the time taken to achieve clinical union was also assessed. Clinical union was defined as a bridging callus or callus exceeding 50% of the tibial diameter at the fracture site, visible on at least three out of four cortices in two standard radiographic views (Guiot & Déjardin, 2011).

Table 2.

Radiographic scoring system based on callus formation, appearance of the fracture line, and stage of union used to determine a fracture healing grade as a means to monitor dogs that underwent Pedicle screw-Rod for the fixation of tibial osteotomy (Whelan et al., 2002).

Variable	Grade of fracture healing
	1	2	3	4	5
Callus formation	Homogeneous bone structure	Massive bone trabeculae crossing fracture line	Apparent bridging of fracture line	Trace or no bridging of fracture line	No callus formation
Fracture line	Obliterated	Barely discernible	Discernible	Distinct	Distinct
Stage of union	Achieved	Achieved	Uncertain	Not achieved	Not achieved

2.7.2. Alignment and fragment apposition

Evaluation of tibial length and alignment in the frontal and sagittal planes included measuring the mechanical medial proximal and distal tibial angles (mMPTA and mMDTA, respectively) and evaluating tibial valgus and the Tibia plateau angle (TPA) at three time points: before osteotomy on the intact tibia, immediately after surgery, and finally at the time of implant removal. The mMPTA and mMDTA measurements were taken on caudocranial radiographs using the established method (Dismukes et al., 2007). The calculation ([mMPTA + mMDTA] - 180) was utilized to determine the post-operative valgus angle (Guiot & Déjardin, 2011). TPA was assessed on the mediolateral view following the method outlined by Warzee et al. (Warzee et al., 2001). Computer software (efilm Workstation, v4.2, MERGE Healthcare, Chicago, USA) was used to measure alignment angles.

Rotational alignment was qualitatively defined as anatomical when the caudal edges of the medial and lateral tibial plateaus overlapped, and the talar trochlea ridges were concentrically projected on lateral radiographs. In contrast, any metatarsal angulations ≥ 10° deviating from the limb's sagittal plane were deemed indicative of unacceptable tibial rotational malalignment (Guiot & Déjardin, 2011).

In this study, the osteotomy was carried out prior to bone fixation, allowing the surgeon direct vision of the osteotomy site. Bone fragment apposition, indicating the excellent replacement of fracture segments in their original anatomical position, was expressed as a percentage of apposition of the two ends of the bone in the osteotomy area. We aimed to align the proximal and distal tibial fragments with an ideal apposition while maintaining a consistent gap distance.

2.7.3. Implant

The position and integrity of the implant were assessed weekly through radiological examinations during the bone healing process until implant removal. Radiographic evaluations were conducted weekly to monitor screw loosening using a grading score system ranging from 0 to 4, which assessed the radiolucency around all screws (Ganser et al., 2007).

2.8. Statistical analysis

Initially, the data were checked for normality with the Shapiro-Wilk test. Data with normal distribution were analyzed with the repeated measure test (mMDTA, tibial valgus), while non-parametric and qualitative data were analyzed with Friedman's Two-Way test (lameness grading score system, radiographic scoring system, mMPTA, TPA). Normally distributed data were presented as (mean ± standard deviation), while non-parametric data were shown as median (interquartile range). All statistical analyses were conducted using SPSS software (version 27 for Windows, SPSS Inc., Chicago, IL, USA) by an expert statistician, and a value of P < 0.05 was considered significant.

3. Results

3.1. Clinical evaluation

All animals began bearing weight on the operated limb 24 h after surgery. Throughout the recovery period, no complications, such as SSI, erythema, self-mutilation, or sinus tracts were noted. The fixation apparatus remained fully functional, with no issues in its components, throughout the healing period until its removal from the affected tibia. There were no instances of premature screw loosening or loosening at the Pedicle screw-Rod junction in the fixation device. According to the lameness grading score system, the average value of each parameter (Table 1) gradually decreased to one (the most ideal state) within 21 days after surgery in all dogs, (Fig. 2; Supplementary files 1 and 2). The results of the statistical analysis of lameness grading scores showed a significant trend in all four evaluated parameters within 21 days (Fig. 3).

Fig. 2.

Postoperative evaluations indicate that normal ambulation and pain-free weight-bearing were achieved 21 days after the operation.

Fig. 3.

Clinical evaluation of the lameness grading score system in all studied animals (A-D). The evaluation included walk and trot (A), standing (B), raising the intact contralateral Limb (C), and pain in palpation (D). Statistical analysis showed P-value = 0.001 for all four parameters, indicating a significant decreasing trend over time for each parameter.

3.2. Radiographic evaluation

The radiographic scoring system demonstrated the healing progress at all osteotomy sites (Fig. 4). Statistical analysis of the results showed that there was a significant trend over time (Fig. 5). The mean ± standard deviation (SD) of clinical union was 5.8 ± 1.30 weeks, ranging from 4 to 7 weeks, while complete radiological bone union occurred at 11.4 ± 1.51 weeks, ranging from 10 to 13 weeks after PS-R implantation.

Fig. 4.

Mediolateral (A–C) and caudocranial (D–F) radiographs of dog No. 5, a 20 kg mixed-breed dog. Preoperative radiographs of the intact tibia are shown in (A) and (D). Immediately postoperative radiographs indicate that osteotomy healing, assessed using the radiographic scoring system, was graded as 5 (B and E). At 10 weeks post-operation, radiographs show osteotomy healing graded as 2 (C and F). Limb alignment in both the frontal (A–C) and sagittal (D–F) planes was achieved. Postoperative rotational alignment was anatomical (B and C), with satisfactory fragment apposition observed (C and F). The complete unity of the bone was evidenced by the full restoration of cortical and medullary continuity (C and F), with no radiolucency observed around the screws. This finding indicates superior binding at the bone-screw interface (F).

Fig. 5.

Postoperative radiographic union scoring for all studied animals. Statistical analysis revealed a P-value = 0.001, indicating a significant decreasing trend over time.

Postoperative mMPTA and mMDTA were 92.00° (92.00°, 91.50°), ranging from 91° to 92°, and 93.40° ± 1.14°, ranging from 92° to 95°, respectively. The median (interquartile range) of postoperative TPA was 22.00° (23.00°, 22.00°), ranging from 22° to 23° The mean ± SD of postoperative tibial valgus was 5.20° ± 1.48°, ranging from 3° to 7° Bone alignment in both the frontal and sagittal planes was achieved in all animals (Fig. 4). Furthermore, upon re-evaluation of tibial alignment, including mMPTA, mMDTA, tibial valgus, and TPA during the final assessment at the time of implant removal, the values remained consistent with those measured immediately after surgery (Fig. 4). Statistical analysis of bone alignment data (tibial alignment angles) at three time points (pre-operation, post-operation, and implant removal) revealed no significant differences in any of the measured angles (TPA, mMPTA, mMDTA, and tibial valgus) across these time points (Table 3).

Table 3.

Tibial alignment angles in the frontal and sagittal planes were measured at three different time points. Data with a normal distribution are presented as mean ± SD, while data with a non-normal distribution are expressed as the median and interquartile range. In the statistical analysis, no significant differences were found in the angles measured at different time points. A value of P < 0.05 was considered statistically significant.

Tibial joint angles	Pre-operation	Post-operation	Implant removal	P value
TPA (°)	23.00 (23.00, 22.00)	22.00 (23.00, 22.00)	22.00 (23.00, 22.00)	0.717
mMPTA (°)	92.00 (92.00, 90.50)	92.00 (92.00, 91.50)	92.00 (92.00, 91.50)	0.135
mMDTA (°)	93.20 ± 0.83	93.40 ± 1.14	93.40 ± 1.14	0.621
Tibial valgus (°)	4.60 ± 1.34	5.20 ± 1.48	5.20 ± 1.48	0.700

The postoperative radiographic rotational alignment was characterized as anatomical, with no significant rotational malalignment observed in any cases. Bone fragment apposition showed that the proximal and distal tibial fragments at the osteotomy site were apposed 90–100% of the mid-diaphyseal tibial diameter, indicating satisfactory replacement in all dogs (Fig. 4).

Assessment of PS loosening (radiolucency at the bone-screw interface) revealed no loosening in either the proximal or distal screws at any of the application sites throughout the entire study period (Fig. 4, F).

4. Discussion

We assessed the effectiveness of the monoaxial PS-R configuration as an external fixation method for non-articular tibial diaphyseal osteotomy. Our study indicates that the unilateral application of the PS-R configuration, using minimally invasive techniques, is a successful and versatile approach for fixing experimentally induced tibial fractures.

Irrespective of the specific surgical fixation method chosen for motor limb fractures, it is crucial to achieve regular limb length, proper bone alignment in all planes, functional limb positioning, correct joint alignment, appropriate limb rotation, and improved overall limb appearance to facilitate the patient's functional recovery (Dismukes et al., 2007; Guiot & Déjardin, 2011; Krettek et al., 2001). Conversely, in MIO techniques, the main challenge lies in addressing postoperative malalignment, due to the limited visibility of the fracture region (Guiot & Déjardin, 2011).

Angular deformities and malalignment of the tibia can result in the improper distribution of forces to adjacent joints, resulting in joint malalignment. This malalignment may contribute to or result from conditions such as cranial cruciate ligament disease and patellar luxation in dogs, ultimately leading to osteoarthritis, lameness, and discomfort (Dismukes et al., 2007; Dismukes et al., 2008; Kettelkamp et al., 1988).

Sherman et al. conducted a study assessing the application of linear external skeletal fixation in a minimally invasive manner for stabilizing non-articular tibial fractures in dogs and cats. Following postoperative evaluations, they determined that tibial alignment in the frontal and rotational planes was satisfactory. However, bone alignment in the sagittal plane did not fall within the expected range. Despite this, their study reported no adverse outcomes during the final follow-up assessments (Sherman et al., 2023). Another investigation examined the fixation of non-articular tibial fractures using the MIPO technique, noting successful tibial alignment across all planes (Guiot & Déjardin, 2011). Cabassu's research also documented satisfactory postoperative tibial alignment in all planes for tibial diaphyseal fracture fixation using the MIPO technique, even without intraoperative imaging. Nevertheless, 12% of the patients required immediate reoperation (Cabassu, 2019). Our study's results align with those of Sherman et al. and Guiot & Déjardin, confirming successful tibial alignment across all planes postoperatively. In the present study all measured angles (mMPTA, mMDTA, TPA) fell within the normal range established for dogs, as documented in previous studies (Dismukes et al., 2007; Fettig et al., 2003). However, our findings differ from Cabassu's, as none of our patients required reoperation. This discrepancy may stem from the lack of intraoperative imaging and the limited visibility of the fracture area associated with the MIPO technique. In our investigation, the osteotomy was performed before bone fixation, allowing the surgeon direct visualization of the osteotomy site.

As indicated by prior research, iatrogenic factors, including incorrect application of fixation apparatus, are identified as potential contributors to angular limb deformities, bone malalignment (malunion), delayed union, and non-union (Dismukes et al., 2007; Kettelkamp et al., 1988). Singh et al. evaluated the outcomes of long bone fracture fixation using a linear skeletal external fixator in 17 dogs, finding five cases of delayed bone union, four cases of non-union, and one case of malunion (Singh et al., 2023). In our investigation, we assessed tibial alignment parameters, including mMPTA, mMDTA, tibial valgus, and TPA. Comparing tibial alignment angles, the results did not indicate any differences at each evaluated time point. In contrast to Singh et al.'s findings we confirmed that the PS-R configuration performed well, providing sufficient strength regarding bone alignment stability throughout the healing period. There are several possible explanations for this discrepancy, which can be attributed to the improper use of the fixation device and its insufficient strength.

In the study by Singh et al. on the use of skeletal external fixators for long bone fractures, patient weight-bearing performance was assessed using a scoring system. Results indicated that the first weight-bearing occurred on the 20th day post-operation (Singh et al., 2023). In contrast, the results of our study differ from those of Singh et al. In our study, all patients were able to bear weight on the affected limb 24 h after surgery. In the present study evaluation of the lameness scoring system indicated that, by 21 days after surgery, all patients regained their primary function and normal movement. This discrepancy can be attributed to the extent of damage to the bone and the surrounding soft tissue, which significantly affects bone healing and weight bearing after surgery. In our study, PS-R implantation resulted in minimal damage to the fractured bone and adjacent soft tissues.

Pin-tract infection is a significant complication of external fixation, and its successful treatment can be risky (Beever et al., 2018). Deep pin-tract infections are common in the tibia, potentially due to limited coverage of soft tissue on the medial aspect, poor extraosseous and intramedullary blood supply of the canine tibia (Dugat et al., 2011; Harari, 2002). Complications related to tibial pin-tracts should be anticipated, particularly those associated with the lateral aspect of the proximal full pin in type II skeletal external fixation, primarily due to soft tissue irritation from the implant (Sherman et al., 2023). Tibial pin-tract morbidity can be reduced by the addition of more fixation pins and avoiding proximal lateral pin placement whenever possible (Kraus et al., 1998). Singh et al. evaluated postoperative complications associated with linear skeletal external fixators used for tibia-fibula and radius-ulna fractures. Their study found that osteomyelitis and pin-tract infection were the major postoperative complications (Singh et al., 2023). Sherman et al. conducted a similar study examining postoperative complications associated with minimally invasive linear external skeletal fixation for stabilizing non-articular tibial fractures in dogs and cats. Their study found that 40% of cases experienced postoperative complications, primarily related to pin-tract morbidity, including swelling, erythema, and discharge (Sherman et al., 2023). Our study's findings are not consistent with those of Singh et al. and Sherman et al. In our research, no complications, such as infection or drainage, were observed at the screw insertion site. This discrepancy could be attributed to the unilateral placement of the screws solely on the bone's medial aspect or the high strength of the fixation device, which prevents micro-motion at the screw insertion site.

Previous research on external skeletal fixation assessed the extent of pin loosening by analyzing the radiographic presentation of bone resorption around the pins (Ganser et al., 2007; Sherman et al., 2023; Zheng et al., 2011). This radiolucency indicates bone resorption around the pins, leading to a weakened bond between the bone and the stabilizing implant. Sherman et al. conducted a study evaluating radiographic pin loosening in 75 cases of minimally invasive stabilization of non-articular tibial fractures in dogs and cats using linear external skeletal fixation. Their study found that 18% of cases showed radiographic evidence of pin loosening (Sherman et al., 2023). In contrast, our study found no evidence of loosening at the proximal or distal screw insertion sites during radiographic evaluation. This difference may be due to the adequate strength of the stabilizing device, the design of the screw (including its threads), or the material used for the screws.

Sun et al. examined the impact of PS made from stainless steel and titanium on the bone-screw interface. Their study determined that titanium screws exhibited superior binding at the bone-screw interface compared to stainless steel screws, with biomechanical tests for torsional strength and pull-out resistance also favoring titanium (Sun et al., 1999). In another study investigating pin loosening in unilateral external fixation, two types of half pins made from different titanium alloys, Ti2448 (Titanium 2448) and TAV (Titanium-6, Aluminium-4, Vanadium), were compared. The study concluded that Ti2448 half pins increase osseointegration and reduces pin loosening compared to TAV half pins (Zheng et al., 2011). Ganser et al. compared stainless steel and titanium Schanz screws for external fixation, finding no significant clinical benefit in using either type to reduce pin loosening or pin-track irritation/infection (Ganser et al., 2007). We cannot comment on this comparison, as all screws in our study were titanium. In our study, all screws remained intact without loosening, bending, or breaking throughout the weight-bearing period.

Dudley et al. investigated the timing of clinical union in 47 dogs with tibial fractures, comparing two treatment methods including open reduction with bone plate stabilization and closed reduction with external fixation. Their results indicated that clinical union was achieved in 87–121 days for the open reduction with bone plate stabilization method, while the closed reduction with external fixation method achieved clinical union in 69–82 days post-operation (Dudley et al., 1997). In a similar study, Guiot and Déjardin evaluated the time to clinical union in minimally invasive plate osteosynthesis for 36 non-articular tibial fractures in dogs and cats. Their findings indicated that clinical union was achieved 36 to 45 days post-operation (Guiot & Déjardin, 2011). The results of our study contradict those of Dudley et al., but closely align with the findings of Guiot and Déjardin. In our investigation, the assessment of healing time revealed that clinical union was achieved 28 to 49 days post-operation. In Sherman et al.'s study, which investigated the effects of linear external skeletal fixation using a minimally invasive method, complete bone union and removal of the fixator occurred in 71 ± 48 days (Sherman et al., 2023). The results of our study are not consistent with those of Sherman et al. In our investigation, complete bone union and fixator removal occurred in 80 ± 11 days. This inconsistency may be attributed to variations in bone stabilization methods, the types of fractures, the extent of damage to the bone and surrounding soft tissues, and the individual characteristics of the animals studied across different research.

The present study had several limitations. Firstly, the small sample size was due to ethical considerations. Additionally, there was no control group or alternative treatment group for tibial fractures to allow comparison of results. The study also lacked biomechanical evaluation of the implant in long bones under laboratory conditions. Furthermore, it did not assess the implant's biocompatibility with bone and adjacent soft tissues, including the examination of bone healing patterns, neovascularization at the fracture site, and osseointegration at the bone-screw interface. These factors could be evaluated using non-invasive diagnostic imaging techniques such as ultrasonography and micro-CT, or invasive methods like histology. This research serves as a preliminary study to assess the efficacy, performance, and feasibility of the PS-R configuration as an external fixation method for canine tibial osteotomy. Future studies should incorporate these additional evaluations to gain a more comprehensive understanding of the technique's efficacy.

5. Conclusion

In conclusion, the results of this study demonstrate that it is technically feasible to fix non-articular tibial osteotomies using a PS-R configuration. No complications were observed during the evaluation of the healing process throughout the recovery period. The PS-R configuration can be considered a relatively simple, quick, affordable, accessible, yet rigid and effective technique for stabilizing experimentally induced tibial fractures. A comprehensive evaluation of this method, including a direct comparison with other standard tibial fixation techniques under identical conditions, is recommended.

Funding

This study was supported by the Vice Chancellor of Research and Technology at Urmia University.

Ethical statement

Dogs were used for research purposes, with informed consent obtained and full knowledge of the animal shelter directorate. The Research Ethics Committee of Urmia University (IR.URMIA.REC) reviewed and approved this study (Urmia, Iran, Faculty of Veterinary Medicine, Ref: IR-UU-AEC-3/79). Furthermore, the study adhered to the ARRIVE guidelines (Animals in Research: Reporting In Vivo Experiments).

Declaration of generative AI and AI-assisted technologies in the writing process

During the preparation of this study, the authors used ChatGPT to rewrite some parts of the manuscript. After using this tool/service, the authors review and edit the content if needed and take full responsibility for the content of the publication.

Consent for publication

Informed consent for the publication of identifying images or other personal or clinical details was obtained from all participants.

CRediT authorship contribution statement

Mohammad Mahdi Gooran: Writing – original draft, Investigation, Formal analysis, Conceptualization. Ramin Mazaheri-Khameneh: Writing – review & editing, Supervision, Project administration, Methodology, Conceptualization. Seyed Mohammad Hashemi-Asl: Writing – review & editing, Investigation, Data curation. Rahim Hobbenaghi: Writing – review & editing, Investigation.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

• The data that support the findings of this study are available from the corresponding author upon reasonable request.