Virtually Reconstructing Bernhard Heine’s Osteotome

Abstract

The osteotome was a hand-cranked medical chainsaw designed in 1830 by the German surgeon Bernhard Heine. Before Heine, surgeons used crude, manual tools, such as hammers, chisels, and handsaws. The osteotome was among the first mechanical tools used in orthopedic surgery, and it preceded the later use of the motorized chainsaw for woodcutting. Due to the small number of units manufactured, questions remain about the osteotome’s usage. To facilitate conservation and assist with investigation, Heine’s osteotome was digitally reconstructed. As with other digital reconstruction attempts in cultural heritage, assumptions were made to facilitate reproduction. To highlight the functional similarities and contrasts between early and contemporary tools, its parts were compared with contemporary chainsaws and surgical tools. Contemporary orthopedic surgeons have largely shifted away from medical chainsaws, such as the osteotome, in favor of reciprocating saws. Due to its small size and medical purpose, the osteotome was designed for greater precision than a modern industrial chainsaw. Based on the reproduction and comparative analysis, the device was likely used in a manner more similar to modern medical reciprocating saws than to its direct descendant, the industrial chainsaw. The Heine osteotome mechanized surgery and its descendants are still used in medicine and the industry. The osteotome model enabled an analysis of its function and use.

1. Introduction

1.1. Overview

The osteotome was a hand-cranked chainsaw designed in 1830 by the German surgeon Bernhard Heine to cut through bone [1,2]. It was a significant advance in orthopedic surgical tools and a direct improvement over prior practice [3]. As nightmarish as it may look, it was far less painful for patients than other tools used for amputations, such as the combination of hammer and chisel or the hacksaw. Osteotomes were produced in small numbers for much of the 1800s, so only a few remain [4]. The reverse engineering of cultural heritages has consisted in the experimental reconstruction from primary sources and the restoration of artifacts, where assumptions are made to facilitate reproduction [5,6]. As the Heine osteotome heralded the mechanization of surgery and invention of the chainsaw, its legacy endures in contemporary surgery and industry. To facilitate the preservation and restoration of these surgical devices, a Heine osteotome was digitally reconstructed for this study.

1.2. Background

1.2.1. Tool Summary

The significance of the osteotome was its role in mechanizing medical procedures. Prior to the osteotome’s invention, orthopedic surgery was conducted with hand tools, including hammers, chisels, and saws. As bone is a strong, rigid material, constant pressure is necessary for a successful cut. Hand tools required manual effort, resulting in an imprecise, inconsistent application of force [7]. This lack of consistent force and applied pressure could result in patient injury, extreme discomfort, hemorrhaging, and complications during surgery. The use of mechanical tools in orthopedic surgery changed this. The osteotome was the first such tool, and its impact as a technological innovation extended well beyond medicine [1,8]. The modern industrial chainsaw traces its roots to the Heine osteotome, which was shaped by the requirements of orthopedic surgery.

1.2.2. Surgical Requirements

Orthopedic surgery required a precise application of force to break, cut, and remove bone. Different types of bone include trabecular and cortical ones, each with specific properties. Bone actively reshapes itself in response to pressure. Cells called osteoblasts thicken bone, while cells called osteoclasts break down bone. Both cells require blood vessels for nutrient delivery and waste removal [9,10]. A bone regularly exposed to stress will thicken. A bone without regular exposure to stress becomes thinner and weaker, eventually leading to osteoporosis. Bone spurs and fragments can lead to pain. Similarly, infection can require surgical osteotomy, or cutting a section of bone.

Such surgical procedures necessitated applying pressure along a narrow, sharpened edge to break, saw, or shatter bone. Removal of damaged material was required in order to prevent the formation of bone spurs [11]. The proximity of blood vessels, which sustain bone growth, also required care to avoid unnecessary bleeding. Similarly, exposed blood could facilitate the spread of infectious pathogens [8,10,12].

1.2.3. Manual Tools

In pre-modern times, orthopedic surgeons often used similar tools to those used by carpenters, butchers, and other artisans, who often were the only surgeons available. Manual tools used in carpentry included hammers, chisels, handsaws, and drills [13]. Butchers possessed cleavers and heavy blades for cutting through bone and finer blades to slice through skin and muscle. The use of these tools in surgery was risky, even before considering sterilization and the almost complete absence of anesthesia [8,13].

The manual positioning of tools, often by holding them steady and in a fixed position, was challenging. An incision in the skin was made with a small blade, and then a larger tool was used. A chisel would be placed edge-down against the bone before being repeatedly struck with a hammer. A saw would be dragged repeatedly across the bone. A drill would be positioned above the target point and turned by hand. Other tools from carpentry and butchery could similarly be applied to human flesh [13]. Amputation was not uncommon, as a festering infection could turn septic and spread to the heart [10,12].

Manual surgery devices were not always improvised tools. Some doctors in antiquity and the early modern period, such as Galen and Paracelsus, possessed surgical instruments resembling their modern counterparts [13]. Evidence of “modern” medical devices, such as scalpels and syringes, is not unique to Europe and can be found worldwide [13]. However, the scientific and industrial revolutions were required to truly codify modern medical practices. The osteotome resulted from the application of modern practices to traditional needs [1,12]. The osteotome is the direct forerunner of contemporary orthopedic tools.

1.2.4. Contemporary Orthopedic Tools

Contemporary orthopedic tools are surgical versions of power tools from other fields. While surgical chainsaws existed historically, electric rotary and reciprocating saws fill a similar contemporary niche. Electric drills, with a greater variety of drill bits and diameters, took the place of their hand-cranked counterparts [11]. Other devices, such as clamps and pins, are largely unchanged in form. However, they may be made of modern materials [13]. Such tools are used in orthopedic and dental surgery [1,14]. While no longer a widespread surgical tool, the contemporary chainsaw is a widespread industrial tool.

1.2.5. Contemporary Chainsaws

While widely used in forestry and lumber operations, a variety of chainsaws are also used in the modern industry. Concrete-cutting chainsaws are used in construction [15,16]; chainsaws powered by both electric and combustion engines are used for woodcutting. Retail models are typically operated by one person, while industrial ones used for tree felling may require more than one operator [17].

Contemporary industrial chainsaws share part of their terminology. For example, “choke” refers to a valve obstructing air flow in a combustion model. The “bar” refers to the blade of the chainsaw, around which the chain rotates. The “teeth” refer to the sharpened links in the chain that cut and move away material. Saws produce a force called kickback while cutting, requiring careful handling [16]. Kickback typically results from attempting to cut a dense material or failing to apply constant pressure. The upper part of the bar was traditionally the highest-risk area for kickback. Kickback can result in damage to the chainsaw or operator injury [15,16]. Commercial models often include a sprocket at the front of the bar to reduce the risk to the operator [18]. Understanding comparable mechanical saws in contemporary industry and surgery was essential in comparing them to Heine’s invention.

2. Materials and Methods

2.1. Research Methodology

Due to a scarcity of original models, the osteotome was reconstructed based on photographs and other online and archival sources. A virtual model was developed from these sources. Due to separate models, sizes, and manufacturers, the exact specifications of each device were unknown. Graphical depictions, commentary on Heine’s diagrams and descriptions, and the prior literature were examined. The gathered material was used to ensure that the model was kept as close to Heine’s original design as sources allowed [1,14].

An online search was conducted to acquire additional information. A search for keywords, phrased as “Heine chain osteotome”, was conducted using Harzing’s Publish or Perish v.4 software (Harzing, London, UK). The results were further filtered by searching for the words “Heine” or “osteotome” in the title. Photographs, diagrams, and images of the device were sought in the search results. English-language documentation on its use was also sought.

In addition, an image search was conducted using Google and DuckDuckGo. The search phrase was “Heine osteotome”. Visual inspection was used to locate the relevant images, assisted by the tool’s distinctive shape. A directory was filled with relevant images depicting hand-cranked osteotomes. However, no meaningful units of measure were included in these retrieved photographs, which lacked specific dimensions, as shown in Figure 1.

Archival sources suggest that since the initial version in 1830, osteotomes bore slight variations between manufacturers. A photograph from the late 19th or early 20th century (Figure 2) of a surgeon holding an osteotome was used to estimate its dimensions [1,4,9]. This period was after the peak usage of the Heine osteotome, so it was presumed that the photograph was instructive [1]. The surgeon’s body proportions were estimated based on the height of an average adult male in the Edwardian period [19]. The total length of the osteotome was calculated by comparing the length (in pixels) of the osteotome relative to the surgeon’s arms. All other dimensions were estimated based on this value. Archival diagrams, photographs, and articles were used to estimate the size, location, and function of each component.

2.2. Digital Replication

Reconstruction was performed in SolidWorks 2018 (Dassault Systems, Vélizy-Villacoublay, France). Approximate component sizes were input in CAD and adjusted as necessary to fit. The completed model was saved in the SolidWorks format as well as in the STEP (.stp) file format. The STEP format is commonly used in CAD. It stores separate objects and related information [20]. For example, each component can be stored with different texture meshes. The STEP format can be converted into other formats relatively conveniently. Each component was stored as a separate mesh object, with the distance and connected parts stored within the STEP file.

2.3. Chainsaw Comparison

The digital reconstruction was compared to a relatively contemporary chainsaw, in particular a Homelite XL-12 [18]. The comparison entailed a visual inspection of analogous parts to determine similarities and differences in ergonomics, usage, and function. While the commercial chainsaw is a product with a different application and design, it provided an example of how far the technology has developed.

The use of contemporary powered saws in orthopedic surgery was considered. Contemporary surgeons use powered reciprocating and oscillating saws, which can be used in a single hand [7]. Contemporary surgeons may apply a second hand for stability, but two-handed use is not essential. Unlike contemporary devices, the Heine osteotome required two hands, one to turn the crank and the other to hold the device [9,11]. However, the compact size, single-handed grasp, and external power sources marked greater structural changes in form and function. Understanding the historical and contemporary surgical contexts enables a direct understanding of the Heine osteotome’s innovative role in mechanizing surgery. Thus, a Heine osteotome shares more mechanical similarities with a contemporary chainsaw than a contemporary powered bone saw.

3. Results

3.1. Model Overview

A virtual osteotome was reconstructed in SolidWorks 2018 software. From the tip of the handle to the end of the cutting teeth, the total length of the device was 428.7 mm. The tip of the guide rod added another 2.3 mm. The total device length, including the guide rod, was 430 mm. As shown in Figure 3, the fully assembled model included a rear handle (the “dagger grip”), a foregrip/front handle (perpendicular to the sprocket), a bar (the “blade”), a crank (opposite the front handle or foregrip), a guide rod (a slanted rod above the bar), and a chain (around the bar).

Despite the sword-like appearance shown in Figure 4A, the components corresponded to those of a modern chainsaw. The interior is shown in Figure 4B.

The device was used in a similar manner to powered bone-cutting surgical equipment, such as a contemporary reciprocating or oscillating saw. After an initial incision, the cutting teeth were placed against the bone. The front brace was used to steady the bar (the equivalent of the blade of a chainsaw) as the surgeon applied pressure to the rear handle and moved the crank [21]. The interior parts are visible in the cross section in Figure 4B.

The crank was axially connected to a sprocket. The teeth of the sprocket fit between chain links, causing the chain to move. The teeth would carry away bits of material, precluding the surgeon from having to constantly readjust. Prior bone-breaking techniques, such as the impact of a hammer and chisel or the use of a handsaw, were less precise than the osteotome.

3.2. Chainsaw Component Comparison

3.2.1. Summary

The chainsaw and the osteotome have superficial similarities, but also key differences. The first difference is the increased length and weight of the modern chainsaw, as it is intended for woodcutting [17]. The second is the replacement of the manual crank with a motor to power the chain. Highlighting the individual function and purpose of each sub-assembly is integral to understanding the osteotome’s function. Four primary assemblies are compared below: the grip, the bar, the chain drive, and the chain.

3.2.2. Grip

The grip consists of all the handles grasped by the user. In the case of the chainsaw, the grip is located entirely at the rear of the device. As shown in Figure 5, the osteotome had a foregrip perpendicular to the bar and a “dagger” grip in the rear, seemingly in a convergent design with the chainsaw. At first glance, the osteotome possesses three grips: the “dagger grip”, the foregrip/front grip, and the crank. In the osteotome, the foregrip handle is perpendicular to the “dagger grip” and opposite to the crank. In Figure 2, the surgeon leaned into the osteotome, using an extension of the “dagger grip”. This was intended to allow the user to more easily leverage their body weight for the cutting process [17].

However, Figure 2 shows the osteotome’s “dagger” grip with a wooden extension braced against the chest. As the object being cut in Figure 2 is a skeleton, the usage context appears to be instructive or demonstrative, instead of a genuine surgery [14]. The use of such a brace could enable a greater use of the surgeon’s body weight to assist in cutting. The shorter length of the osteotome, relative to the chainsaw, allows for greater precision. Precision is far more important in surgery than in woodcutting [13].

3.2.3. Bar

The bar consists of the dagger-like “blade” of the chainsaw, i.e., the area around which the chain rotates. In the chainsaw, the bar is longer, allowing for an extended cutting reach. The chainsaw bar is also wider, allowing it to sustain greater force [15,16]. The osteotome’s bar is triangular, whereas the chainsaw’s bar is rectangular.

As shown in Figure 6A, the dagger shape of the osteotome has a narrower point of contact with the cutting surface. Above the osteotome is a “guide rod”, which allows for additional support when braced against a cutting surface. The guide rod may enable systematic clearing of residual material dragged along by the chain, in addition to securing the cutting direction.

3.2.4. Chain Drive

The chain drive consists of the mechanism that cycles the chain. In the osteotome, the chain is rotated by a sprocket connected to a hand crank. In the chainsaw, the chain is rotated by a motor, often gasoline or electric [15,16,17]. The chainsaw requires power and space for the motor, as well as a frame able to provide sufficient structural support.

As shown in Figure 6A, the sprocket that moves the osteotome’s chain is positioned at the rear center of the bar, directly connected to the hand crank. A smaller sprocket is positioned at the front of the cutting tip, to reduce friction and kickback. In the osteotome, the diameter of the front sprocket is ~1/3 the size of the main sprocket, resulting in a substantial mechanical advantage. The chainsaw’s drive is at the rear of the bar, near the engine [17]. This reduces the transmission power loss. For both devices, the sprocket that moves the chain is positioned where it is most mechanically efficient.

The cutting rate for both instruments depends directly on the drive sprocket’s rotations. There is a direct correlation between the rotations per minute (rpm) of the drive sprocket and the power source’s output. This rate is directly proportional to the engine’s power in the chainsaw and to the rate of manual cranking in the osteotome. Other factors affecting the total rpm are the length of the chain and the resistance of the object being cut [15,18]. While a manual osteotome may have a lower maximum rpm, the shorter chain may prove sufficient for cutting through the intended object. Similarly, the lower speed means less potential unintended energy transfer from vibration [17].

3.2.5. Chain

The chain consists of component links, some equipped with cutting blades. A wide range of chain links are used in chainsaws, often depending on the industry or application. Diamond-tipped chains are used to cut metal in salvage operations [16], while blunter chains are used to cut concrete [15]. In the case of wood, diamond-shaped blades are used [17]. As a specialized surgical instead of an industrial one, the osteotome lacks a variety of specialized chains.

Photographs from cited sources detail chain link geometry [14,21]. As shown in Figure 6B, the osteotome’s chain links are small, sharp blades. Each has a low surface area, which minimizes the cutting contact area. A lower rotation rate means potentially less erosion on each cutting tooth. As osteotomes were manufactured by hand, replacement of a chain link could be a costly endeavor in terms of both time and money. As it was directly controlled by hand, a surgeon would likely be aware of how deep and effective the osteotome’s cutting was.

4. Discussion

4.1. Model Overview

The chain osteotome revolutionized orthopedic surgery because it greatly improved cutting efficiency, surgical ergonomics, and patient comfort. Today, orthopedic surgeons possess a wide range of mechanical and powered tools, but Heine’s invention was their direct ancestor [1,13].

4.2. Comparison to Hand Tools

The osteotome was an improvement over previous surgical tools. The hammer and chisel, handsaw, and drill were three previously used methods to cut and remove bone, and each had severe shortcomings. The hammer and chisel required not only precise positioning, but also constant readjustment after each impact. The handsaw required constant pressure and repetitive motion—a difficult task unless the target area was completely stationary [7,13]. The drill required precise placement and downward pressure.

The osteotome’s mechanical design allowed for more consistent outcomes. It enabled the surgeon to use his body weight to assist with cutting, while the guide rod and grip facilitated the placement of the cutting teeth [3]. The chain’s identical, mechanical teeth made cutting through tissue more consistent. As such, it helped to bring about the mechanization of medicine [4].

4.3. Comparison to Contemporary Tools

The osteotome shares similarities with both modern medical tools and industrial chainsaws. It possesses components similar to a modern chainsaw, but used in surgery [4]. The Heine osteotome bears greater mechanical similarities to a contemporary chainsaw than to contemporary powered bone saws.

While the osteotome was a distant ancestor of modern medical and industrial tools, it had serious shortcomings, chief among them the rarity of its components. Though it was a well-known surgical tool, only a handful of manufacturers produced it [4], so the replacement of damaged or worn components was difficult. Moreover, the lack of widespread sterilization practices meant that any component could become more easily contaminated and that the contamination could spread as the components moved [13]. The manual crank required physical strength and dexterity, whereas modern tools use motors to allow for more consistent results. Finally, the use of a chain is more mechanically complex than a rotary saw, which is why modern medical devices have moved away from chainsaws [11,13,22].

4.4. Study Limitations

The reconstructed model was based on an approximation of original materials, which were handcrafted and varied in design among manufacturers. Given the appearance and functionality of the device, it is logical to assume that the device was used in a similar manner to contemporary surgical tools: with great care and precision. While mechanically closer to a modern chainsaw than to a modern surgical saw, its usage would be far more constrained than that of a modern power tool. Further research on primary sources may improve model quality.

4.5. Future Work

The osteotome model enabled an analysis of its function and use. The osteotome is an important part of the history of medical devices, especially the mechanization of medicine. Further research is required to more thoroughly understand the evolution of medical tools in the Victorian period. A direct test of a period-accurate reproduction on phantom or donated tissue could also provide valuable insights into its operation and usage.

5. Conclusions

The reconstructed device was released as a resource for researchers, museum curators, and content creators. While it is only an approximation based on secondary sources, the model can be more readily adapted once a greater range of historical specifications are known. We hope that the publication of this paper and the release of our model will spur on such developments. As a medical tool, the Heine osteotome was designed for greater precision than that afforded by a modern chainsaw. Without Heine’s innovation, the field of medical orthopedics would not have developed as it did.