The bone marrow biopsy needle has undergone a century of evolution. Its size and shape have continuously changed with advancements in materials science and manufacturing techniques - from the early bulky manual ring saw (Trephine) to the modern precision Jamshidi-type Trephine needle, and then to the electric/air-powered bone biopsy system. The design of its size has always been centered around the "sufficiently thick to extract tissue + long enough to reach the bone marrow cavity + minimizing trauma" triangular balance.

1. The Classic Jamshidi Trephine Needle - Still the Benchmark for Size to This Day

In the 1960s, Jamshidi et al. improved the traditional Trephine needle, which laid the foundation for the modern size standard of bone marrow biopsy needles: a stainless steel hollow needle with a flat head and a side window (Notch), equipped with a closely fitting stainless steel needle core (Obturator) at the tip, with a slightly raised end of the needle core protruding from the end face of the needle tube to form a cutting guide. Standard Jamshidi size:

• Outer diameter: The mainstream sizes are 11G (3.0mm) and 13G (2.4mm). Some manufacturers also offer 8G (4.2mm) for unconventional bone tumor biopsy in the hematology department.
• Length: Usually available in three sizes: 3 inches (7.5cm), 4 inches (10cm), and 6 inches (15cm), matching the US standard inch system.
• Operating method: After local anesthesia, insert the needle through the periosteum → remove the needle core → insert the needle core back and turn it clockwise to enter the bone cortex → reach the predetermined depth and withdraw the needle core to confirm there is no blood blockage → continue rotating to cut into the tissue core containing bone trabeculae → turn it counterclockwise slightly and withdraw → use a push rod to extract the specimen.

The key to the design of this type of needle lies in the fact that the length of the side opening is exactly equal to the minimum retained length of the expected tissue core (approximately 12mm). The inner diameter of the needle tube is slightly larger than the width of the sampling window to allow the tissue strip to be completely embedded without being compressed or deformed. The wall thickness of 0.35 to 0.45mm stainless steel provides sufficient torsional rigidity.

II. Improving the Manual Biopsy Needle - Incorporating a Lockable Sampling Slot and Depth Scale

Subsequent manufacturers added to Jamshidi:

The surface of the syringe is laser-etched with markings (every 5mm one mark) to facilitate the determination of the needle insertion depth within the bone.

The detachable depth-limiting ring (Color-coded stopper) prevents excessive insertion.

Some models have inner grooves with micro serrations, increasing the grasping rate to over 95%.

"Single Needle Dual Use" design: When the needle core is retained, it can be connected to an injection device to aspirate bone marrow fluid. When the needle core is withdrawn, it can be screwed in to extract tissue - the size specifications are the same as above (11G/13G × 100/150mm).

III. Electric/Pneumatic Bone Biopsy System - Similar Sizes but Optimized Cutting Edges

The Powered Trephine system for electrically-driven bone biopsy operates by using high-speed and low-speed rotation (typically ≤ 800 rpm) to drive a disposable biopsy probe. The outer diameter of the probe remains at 11G to 13G (2.4 to 3.0 mm), and the length is mostly 100mm or 150mm single gauge (the probe can be replaced). Its advantages lie in reducing the fatigue of the operator's wrist, minimizing the patient's pain, and improving the completeness rate of hard bone (elderly/fibrotic) sampling. Some systems are equipped with an internal and external double-tube cutting mechanism (similar to the principle of an automatic biopsy gun but with low-speed heat protection against damage), with an outer diameter that can be slightly narrower to 14G but still wider than the aspiration needle.

It should be noted that the electric system drill generates heat - the specification requires continuous rotation for less than several seconds followed by intermittent cooling to prevent thermal degradation of the bone tissue, which could affect the interpretation of pathological HE and special staining.

IV. Specialized Pediatric Compact Series

A pediatric Trephine/Jamshidi-type needle developed based on the characteristics of children's bones:

The outer diameter is reduced to the extreme limits of 13G (2.4mm), 14G (2.1mm), and 15G (1.8mm) (it becomes difficult to obtain the core tissue at such a fine level).

Available in three lengths: 40mm, 50mm, and 65mm.

The handle is proportionally shrunk for single-handed operation, and the needle core fits more closely, preventing rapid loss of the child's bone marrow fluid.

V. Future Trends of Miniaturization and Visualization Orientation

In recent years, studies have attempted to further refine the biopsy needle to 14G-16G using imaging (ultrasound/CT) guidance in conjunction with vacuum-assisted devices. However, it is widely recognized that the standard diagnostic criteria for hematological malignancies still rely on a ≥11G-13G trephine. The size cannot be infinitely reduced – the pathology department requires at least 3-5 complete cross-sections of bone trabeculae and sufficient hematopoietic cell volume, and very thin needles cannot meet these requirements. Future improvements will mainly lie in coatings (hydrophilic/abrasion reduction), blade geometry (double-peak diamond blade), and integrated depth sensing rather than changing the core gauge and length paradigm.

Looking back at history, the bone marrow biopsy needle has evolved from the original large-diameter manual drill with a circular saw (with an outer diameter of up to 6-8mm, causing significant trauma) to the modern standard of Jamshidi's 11G-13G × 70-150mm. This is a process of size rationalization and functional specialization - being thick enough to extract tissues, long enough to reach the target area, and sharp enough to minimize trauma. This size philosophy has remained unchanged to this day.