Drilling of bone: Effect of drill bit geometries on thermal osteonecrosis risk regions

Design and performance analysis of low damage anti-skid crescent drills for bone drilling

BACKGROUND

With orthopedic surgery increasing year on year, the main challenges in bone drilling are thermal damage, mechanical damage, and drill skid. The need for new orthopedic drills that improve the quality of surgery is becoming more and more urgent.

METHODS

Here, we report the skidding mechanism of drills at a wide range of inclination angle and propose two crescent drills (CDTI and CDTII). The anti-skid performance and drilling damage of the crescent drills were analyzed for the first time. Inclined bone drilling experiments were carried out with crescent drills and twist drills and real-time drilling forces and temperatures were collected.

RESULTS

The crescent drills are significantly better than the twist drill in terms of anti-skid, reducing skidding forces, thrust forces and temperature. The highest temperature is generated close to the upper surface of the workpiece rather than at the hole exit. Finally, the longer crescent edge with a small and negative polar angle increases the rake angle of the cutting edge and reduces thrust forces but increases skidding force and temperature. This study can promote the development of high-quality orthopedic surgery and the development of new bone drilling tools.

CONCLUSION

The crescent drills did not skid and caused little drilling damage. In comparison, the CDTI performs better in reducing the skidding force, while the CDTII performs better in reducing the thrust force.

Optimizing milling parameters based on full factorial experiment and backpropagation artificial neural network of lamina milling temperature prediction model

BACKGROUND

Milling operations of laminae in spinal surgery generate high temperatures, which can lead to thermal injury and osteonecrosis and affect the biomechanical effects of implants, ultimately leading to surgical failure.

OBJECTIVE

In this paper, a backpropagation artificial neural network (Bp-ANN) temperature prediction model was developed based on full factorial experimental data of laminae milling to optimize the milling motion parameters and to improve the safety of robot-assisted spine surgery.

METHODS

A full factorial experiment design were used to analyze the parameters affecting the milling temperature of laminae. The experimental matrixes were established by collecting the corresponding cutter temperature Tc and bone surface temperature Tb for the milling depth, feed speed and different bone densities. The Bp-ANN lamina milling temperature prediction model was constructed from experiment data.

RESULTS

Increasing milling depth increases bone surface and cutter temperature. Increasing feed speed had little effect on cutter temperature, but decreased bone surface temperature. Increasing bone density of laminae increased cutter temperature. The Bp-ANN temperature prediction model had best training results in the 10th epoch, and there is no overfitting (training set R= 0.99661, validation set R= 0.85003, testing set R= 0.90421, all temperature data set R= 0.93807). The goodness of fit R of Bp-ANN was close to 1, indicating that the predicted temperature was in good agreement with the experiment measurements.

CONCLUSION

This study can help spinal surgery-assisted robot to select appropriate motion parameters at different density bones to improve lamina milling safety.

Avoiding Compartment Syndrome, Vascular Injury, and Neurologic Deficit in Tibial Osteotomy: An Observational Study of 108 Limbs

INTRODUCTION

Tibial deformities are common, but substantial concern may be associated with corrective osteotomy regarding major complications reported in classic literature. Such studies chiefly focused on high tibial osteotomy, with relatively little investigation of other areas and types of deformity. The primary aim of this study was to identify the rate of compartment syndrome, vascular injury, nerve injury, and other major complications after elective tibial osteotomy.

METHODS

One hundred eight tibia osteotomies performed during 2019 to 2021 were evaluated, representing all tibia osteotomies except situations of existing infection. A retrospective chart review was performed to identify patient demographics, surgical indications, anatomic location of osteotomy, fixation used, and complications prompting additional surgery.

RESULTS

The most common osteotomy locations were high tibial osteotomy (35/108 = 32%, 32/35 = 91% medial opening, and 3/35 = 9% medial closing), proximal metaphysis (30/108 = 28%), and diaphysis (32/108 = 30%). The most common fixation was plate and screw (38/108 = 35%) or dynamic frame (36/108 = 33%). Tranexamic acid was administered to 107/108 = 99% of patients and aspirin chemoprophylaxis was used for 83/108 = 86%. A total of 33/34= 97% of anterior compartment prophylactic fasciotomies were performed for diaphyseal or proximal metaphysis osteotomies. No events of compartment syndrome, vascular injury, nerve injury, or pulmonary embolism occurred. One patient required débridement to address infection. Additional surgery for delayed/nonunion occurred for nine segments (8%). Additional surgery for other reasons were performed for 10 segments (9%), none resulting in reduced limb function.

CONCLUSION

Tibial osteotomy can be safely performed for a variety of indications in a diverse range of patients, without a notable risk of the most feared complications of compartment syndrome, vascular injury, and neurologic deficit. Prophylactic fasciotomy and reducing postoperative bleeding using tranexamic acid, along with location-specific safe surgical techniques, may help prevent major complications and thereby facilitate optimized deformity care.

Thermomechanical damage in cortical bone caused by margins of surgical drill bit: A finite element analysis

BACKGROUND AND OBJECTIVE

Conventional surgical drill bits suffer from several drawbacks, including extreme heat generation, breakage, jam, and undesired breakthrough. Understanding the impacts of drill margin on bone damage can provide insights that lay the foundation for improvement in the existing surgical drill bit. However, research on drill margins in bone drilling is lacking. This work assesses the influences of margin height and width on thermomechanical damage in bone drilling.

METHODS

Thermomechanical damage-maximum bone temperature, osteonecrosis diameter, osteonecrosis depth, maximum thrust force, and torque-were calculated using the finite element method under various margin heights (0.05-0.25 mm) and widths (0.02-0.26 mm). The simulation results were validated with experimental tests and previous research data.

RESULTS

The effect of margin height in increasing the maximum bone temperature, osteonecrosis diameter, and depth were at least 19.1%, 41.9%, and 59.6%, respectively. The thrust force and torque are highly sensitive to margin height. A higher margin height (0.21-0.25 mm) reduced the thrust force by 54.0% but increased drilling torque by 142.2%. The bone temperature, osteonecrosis diameter, and depth were 16.5%, 56.5%, and 81.4% lower, respectively, with increasing margin width. The minimum thrust force (11.1 N) and torque (41.9 Nmm) were produced with the highest margin width (0.26 mm). The margin height of 0.05-0.13 mm and a margin width of 0.22-0.26 produced the highest sum of weightage.

CONCLUSIONS

A surgical drill bit with a margin height of 0.05-0.13 mm and a margin width of 0.22-0.26 mm can produce minimum thermomechanical damage in cortical bone drilling. The insights regarding the suitable ranges for margin height and width from this study could be adopted in future research devoted to optimizing the margin of the existing surgical drill bit.

Novel crescent drill design and mechanistic force modeling for thrust force reduction in bone drilling

Bone drilling tends to cause mechanical damages and thermal necrosis in the vicinity of the drilled hole, which can deteriorate the surgery quality and patients' recovery. Understanding the cutting forces generation mechanism is crucial in controlling thrust force and bone temperature for optimum tool design. In this study, a novel crescent drill bit featuring an improved positive rake angle distribution was designed to reduce the thrust force and temperature elevation. On this basis, a mechanistic model for predicting thrust force and torque was proposed for drill bits with different geometries (twist drill and crescent drill). The proposed model was established in the polar coordinate system to precisely calculate the curvilinear integral of the crescent cutting edges. Drilling experiments were carried out using two types of drill bit under different cutting conditions and results showed that our proposed model agrees well with the experimental data. The experimental results also demonstrated that our tool design can significantly reduce the thrust force and reduce the bone temperature below the thermal threshold without coolant, providing a clinical option for coolant free drilling.

JOHNSON–COOK MODEL COMBINED WITH COWPER–SYMONDS MODEL FOR BONE CUTTING SIMULATION WITH EXPERIMENTAL VALIDATION

Constitutive models are widely used to predict the mechanical behavior of different kinds of materials. Although the Johnson–Cook model for bovine bone and Cowper–Symonds model for human thoracic rib and tibia was developed, the predictability of these models was found good only at particular strain rates. This study addresses this lack of information by investigating the Cowper–Symonds model, Johnson–Cook model, and Johnson–Cook model combined with Cowper–Symonds model at different strain rates to utilize in the bone cutting simulation. Specimens prepared using two rear femurs harvested from a 3.50-year-old bovine were investigated at different strain rates (0.00001–1/s). A comparative study made among the stresses predicted from these models showed 29.41%, 10.91%, and 11.11% mean absolute percentage errors using Cowper–Symonds model, and 2.03%, 7.19%, and 3.62% mean absolute percentage errors using Johnson–Cook model, respectively, at 0.0001, 0.001 and 1/s strain rates. However, the Johnson–Cook model combined with the Cowper–Symonds model predicted the stress with a maximum of only 2.03% mean absolute percentage error. The potential of each model to utilize in the orthogonal bone cutting was also evaluated using Ansys® and found that the combined model predicted the cutting force close to experimental cutting force with minimal error (5.20%). The outcomes of this study can be used in the surgical practice and osteotomy procedure before commencing actual surgery.

Thermal effects of various drill materials during implant site preparation-Ceramic vs. stainless steel drills: A comparative in vitro study in a standardised bovine bone model

OBJECTIVES

The aim of this study was to evaluate thermal effects of ceramic and metal implant drills during implant site preparation using a standardised bovine model.

MATERIAL AND METHODS

A total of 320 automated intermittent osteotomies of 10- and 16-mm drilling depths were performed using zirconium dioxide-based and stainless steel drills. Various drill diameters (2.0/ 2.2, 2.8, 3.5, 4.2 mm ∅) and different cooling methods (without/ with external saline irrigation) were investigated at room temperature (21 ± 1°C). Temperature changes were recorded in real time using two custom-built multichannel thermoprobes in 1- and 2-mm distance to the osteotomy site. For comparisons, a linear mixed model was estimated.

RESULTS

Comparing thermal effects, significantly lower temperatures could be detected with steel-based drills in various drill diameters, regardless of drilling depth or irrigation method. Recorded temperatures for metal drills of all diameters and drilling depths using external irrigation were below the defined critical temperature threshold of 47°C, whereas ceramic drills of smaller diameters reached or exceeded the harmful temperature threshold at 16-mm drilling depths, regardless of whether irrigation was applied or not. The results of this study suggest that the highest temperature changes were not found at the deepest point of the osteotomy site but were observed at subcortical and deeper layers of bone, depending on drill material, drill diameter, drilling depth and irrigation method.

CONCLUSIONS

This standardised investigation revealed drill material and geometry to have a substantial impact on heat generation, as well as external irrigation, drilling depth and drill diameter.

Surgical Drill Bit Design and Thermomechanical Damage in Bone Drilling: A Review

As drilling generates substantial bone thermomechanical damage due to inappropriate cutting tool selection, researchers have proposed various approaches to mitigate this problem. Among these, improving the drill bit design is one of the most feasible and economical solutions. The theory and applications in drill design have been progressing, and research has been published in various fields. However, pieces of information on drill design are dispersed, and no comprehensive review paper focusing on this topic. Systemizing this information is crucial and, therefore, the impetus of this review. Here, we review not only the state-of-the-art in drill bit designs-advances in surgical drill bit design-but also the influences of each drill bit geometries on bone damage. Also, this work provides future directions for this topic and guidelines for designing an improved surgical drill bit. The information in this paper would be useful as a one-stop document for clinicians, engineers, and researchers who require information related to the tool design in bone drilling surgery.

Analysis of machining process and thermal conditions during vibration-assisted cortical bone drilling based on generated bone chip morphologies

When the temperature during bone drilling exceeds the safety threshold, the bone tissue surrounding the drilling site can be irreversibly damaged. To investigate the influence of vibration-assisted drilling (VAD) methods on the temperature increase during bone drilling and the causes for temperature increase, drilling experiments were performed on fresh bovine femur samples. The morphology and granularity distribution of the generated bone chips were innovatively used to directly compare the machining processes and thermal conditions of conventional drilling (CD), low-frequency vibration-assisted drilling (LFVAD), and ultrasonic vibration-assisted drilling (UVAD). The experimental results indicated that LFVAD produced the lowest temperature increase of 31.4°C, whereas UVAD produced the highest temperature increase of 44.1°C with the same drilling parameters. Additionally, the morphologies and granularity distributions of the bone chips significantly differed among these methods. We concluded that the smaller temperature increase in LFVAD was mainly attributed to the improved thermal conditions resulting from the periodic cutting/separation motion and the reliable geometric chip-breaking mechanism. In contrast, the unfavourable thermal conditions of UVAD were caused by the higher applied frequency, which created a significantly larger amount of friction heat. This was the main cause for the highest observed temperature increase, resulting in bone crushing processes that generated additional heat.