Construction and validation of a temperature prediction model for cortical bone during orthopedic surgery

Abstract

BACKGROUND: Cortical bone drilling, cutting, friction, and heat generation can easily cause local temperature rise. If it exceeds the bone tissue tolerance threshold and continues to act, it can lead to complications such as bone necrosis, delayed healing, or prosthesis loosening. The coupling of commonly used clinical parameters such as rotational speed, feed rate, and irrigation significantly affects the degree of thermal accumulation, and there is an urgent need to establish a quantitative tool that can predict the temperature field and heat affected zone to define the safe operating window. OBJECTIVE: To establish a temperature prediction model for cortical bone in orthopedic surgery by analyzing the temperature distribution of cortical bone at different depths and radial directions. METHODS: A three-dimensional transient heat transfer control equation was established to describe the cortical bone drilling process. The moving/distributed heat source method was introduced to characterize the interface heat input caused by the shear of the anterior cutting surface and the friction of the posterior cutting surface, and the temperature field evolution at different radial and depth positions was calculated. Using the inverse heat transfer method, the distribution ratio of heat flux and heat between the tool chip bone interface was inverted under the constraint of a finite temperature sequence of measurement points. The model prediction was further validated through experimental comparison. RESULTS AND CONCLUSION: (1) Inverse heat transfer inversion showed that approximately 11.7% of the total heat entered the cortical bone under given conditions; (2) The established temperature prediction model showed good consistency with fresh porcine bone drilling experiments in terms of peak temperature, onset of temperature rise, and temperature-time curve shape, confirming the reliability of the model for spatiotemporal temperature distribution; (3) In terms of spatial distribution, the closer to the hole wall (radius approaching 2.0 mm), the earlier the temperature rise and the higher the peak; along the depth direction (z=0–5 mm), temperature rise first occurred near the surface and gradually extended to deeper parts; (4) The heat affected zone increased with rotational speed: under conditions of drill diameter 4 mm and feed rate 60 mm/min, the heat affected zone was approximately 0.71 mm at 800 r/min and approximately 0.86 mm at 1,000 r/min; (5) These results indicate that under the premise of controlling drill diameter and feed rate, increasing rotational speed increases bone thermal load and heat affected zone thickness; therefore, clinically, rotational speed and cooling/irrigation strategies need to be optimized synergistically to reduce the risk of thermal bone injury; this model can be used for preoperative parameter screening and intraoperative risk assessment, providing quantitative basis for formulating a 'safe parameter window', improving tool and irrigation protocols, and enhancing patient prognosis.

1. Introduction

Cortical bone drilling is a core procedure in orthopedic surgeries such as internal fixation, joint replacement reconstruction, and osseointegrated implant placement. Its safety and precision directly affect postoperative bone healing quality and long-term implant stability [1-7]. Although orthopedic power systems are highly automated, local temperature rise caused by frictional heat during high-speed rotary cutting remains an unavoidable physical risk [8]. Extensive in vitro experiments and animal model studies have shown that if the drilling area temperature exceeds 47 °C for more than 30 seconds, it can trigger osteoblast apoptosis and collagen denaturation; if the peak temperature exceeds 56 °C and persists for several seconds, it will lead to irreversible thermal osteonecrosis, which in turn induces delayed healing, nonunion, and even early loosening of implants [9-11]. Multiple studies have confirmed that the 'temperature-time' dual-variable damage threshold is a key boundary condition for clinical safe operation [12].

However, bone tissue, as a biological composite material with low thermal conductivity (0.32 W/m·K), high anisotropy, and rich moisture content, has much lower thermal conductivity than metals or engineering plastics, making it easier to accumulate heat in semi-enclosed drilling environments [13]. If chips remain in the hole wall and are not effectively cooled in time, they not only hinder heat convection and diffusion but also cause secondary friction and aggravate local temperature rise [14]. A multicenter clinical retrospective analysis found that approximately 19% of early failures after primary total hip arthroplasty were mainly induced by intraoperative drilling thermal injury [15]. Therefore, establishing a predictable and controllable drilling thermal response model has become an urgent need to improve surgical safety and postoperative reliability [16].

Currently, research methods for bone drilling thermal behavior are mainly divided into three categories: experimental temperature measurement, numerical simulation, and hybrid inverse inference. At the experimental level, micro thermocouple arrays, infrared thermal imaging cameras, and fiber Bragg grating sensors are widely used to record transient temperature field distributions under different drilling speeds (500–3,000 r/min), feed rates (20–150 mm/min), drill bit configurations (stepped, hollow, coated), and cooling strategies (external irrigation, internal cooling channels, intermittent drilling) [17-21]. For example, ZHANG et al. [22] used a radial four-point embedded thermocouple method to confirm that in the cortical bone of porcine femur, when the rotational speed increased from 1,000 r/min to 2,500 r/min, the peak temperature at 1 mm from the hole wall increased sharply from 42.1 °C to 68.7 °C, and the depth of the heat-affected zone expanded by 47% simultaneously. LEE et al. [23] used a high-speed infrared camera to capture that under no irrigation conditions, the temperature at the bottom center of the hole could reach (72.3±3.1) °C after 60 seconds of continuous drilling, significantly exceeding the physiological tolerance limit.