From Orthopaedic Museum

The “Sen’s Nail”

Abstract

Orthopaedics in India is developed by many stalwarts by the dint of their inventions and innovations. Sen’s nail is one of them that were invented by Prof. (Dr.) Biswajit Sen from Kolkata, India, in 1973 as a solution to deal with peritrochanteric fractures in elderly. Though the “Sen’s nail” is not in use now a days (because of the advent of newer and better implant and technology for such fractures), it is absolutely imperative to convey to posterity about this lifetime work and obsession of Prof. (Dr.) Biswajit Sen.

INTRODUCTION

In the 1970s when the world was searching to find a solution for peritrochanteric fractures, Prof. (Dr.) Biswajit Sen was conceptualising a surgical procedure that would be with minimal surgical trauma and allied other benefits such as minimum blood loss and very short surgical time and thus could be used for even moribund patients that form a majority of these cases. He also wanted to have a surgical procedure for such fractures by which the elderly (and some even moribund patients) could be mobilised early and thus to avoid a series of postoperative complications faced by available fixation devices in those days. For this, he thought of a long nail to be passed from below upwards taking curvature and contour of the natural morphology of femoral canal and finally to be engaged at the cancellous substance in the femoral head. With these ideas, he then came up with a design of condylocephalic nail, which was later popularised as “Sen’s nail.” For peritrochanteric fractures of femur, the invention of Sen’s nail by Prof. Biswajit Sen was revolutionary.[¹]

CONFIGURATION AND COMPONENTS OF SEN’S NAIL

Sen’s nail is also a condylocephalic nail but completely different from the Ender’s nail. The Sen’s nail was thicker, semi-rigid, and made of stainless steel (SS type 316L). It has two components: the nail and a cancellous lag screw. The nail has three parts: the proximal end, shaft, and distal end. The configuration, components, and parts are shown in Figure 1.

Figure 1: Components of Sen’s nail showing proximal end of 2 cm length (1), shaft (2), cancellous lag screw (3), distal end with ring (4), anterior bowing of nail (5), and starting point of anteversion curve (6)

Proximal end

Its proximal 2 cm is like a triflagged clover leaf in cross-section and thicker (7 mm) in diameter compared with shaft diameter (6 mm) of nail and hence bulbous in shape with blunt tip.

Shaft of the nail

The nail is cylindrical in cross-section with a uniform diameter of 6 mm except the proximal end. The nail has anteroposterior bowing so that it follows the exact contour and curvature of femoral canal. It has also an anteversion curve of 12–15 degrees given 7 cm distal to the tip. Here, it is pertinent to mention that apart from two curves on design, there is slight mediolateral curve also to target abutment on lateral cortex.

Distal end

The distal end is turned upon itself to form a ring through which the medial femoral condyle could be engaged by passing a cancellous lag screw.

Cancellous lag screw

It is a thick cancellous lag screw being used to lock the nail through its distal ring.

WHY IT IS CALLED “SEN’S NAIL”?

The visionary, Prof. (Dr.) Biswajit Sen has lots of inventions in his credit before inventing Sen’s nail, e.g., BD vac drain (Biswajit Sen and Dibyendu Palit vacuum drain), thymectomy for rheumatoid arthritis (RA), transaxillary glenoidal osteotomy for recurrent anterior dislocation of shoulder, intraoral C1-C2 fusion for Koch’s infection, and pathological subluxation of C1-C2 of RA, etc. But none (except one, i.e., BD vac drain) of these inventions had ever named anything. When he invented a nail for peritrochanteric fractures of femur in elderly, his staunch followers out of love had named it as Sen’s nail. This was manufactured by Calcutta Metallic Company.

SURGICAL PROCEDURE: SURGICAL STEPS OF SEN’S NAILING

The entire procedure was done under image intensifier with television (IITV) in Ramakrishna Mission Seva Pratishthan (RKMSP) where Prof. Sen was affiliated. Here it is pertinent to mention that in 1970s, only two institutes/hospitals had IITV in India: one is Bombay Hospital, Mumbai, and other is RKMSP, Calcutta. This procedure was first done in May 1973 at RKMSP, Calcutta. Total approximate time of operation is 20 min and negligible blood loss is 15–20 mL. Various steps of surgical procedure are as follows [Figure 2].

Figure 2: Steps of surgical procedure of Sen’s nail showing landmark of incision (A), making entry point by awl (B), introducing the nail through entry point (C), impaction of nail (D), and final impaction after fine tuning (E)

Incision and portal of entry

After the peritrochanteric fracture of femur being reduced and held on a fracture table, the entry point for the Sen’s nail is determined on the medial femoral condyle. The portal of entry is through a 2 cm long incision along the skin crease starting at a point 2 cm away from the medial border of the patella reaching down to 2 cm above the joint line. The cortex of the medial femoral condyle is bored obliquely (anterolateral direction), and then the entry point is slightly enlarged by toggling the awl.

Introducing the nail

After making entry point, the prebent nail is driven up to the neck, then to be gently rotated to be engaged in to head. The tip of nail ideally should be at the centre of the femoral head in both (anteroposterior and lateral) views and approximately 2.5 mm short of the subchondral bone of the femoral head.

Final impaction

The final position can be fine-tuned further by withdrawing the nail for 5 cm or more and then by abduction/adduction or rotating the limb. After getting satisfactory position, the final impaction of the nail was done after the release of traction on the limb.

Distal locking

Finally, nail is locked into medial condyle of femur by a thick cancellous lag screw (unicortical) without washer through the distal ring in the nail.

HOW IT DIFFERS FROM ENDER’S PROCEDURE

Ender’s procedure used multiple flexible pins and no locking distally. In contrast to Ender’s procedure, only one Sen’s nail was used (because of its larger diameter) with distal locking.

BIOMECHANICS: THE WORKING PRINCIPLE OF SEN’S NAIL

This nail used to work on the three-point fixation principle. The proximal clover leaf end has the hold into the head, the shaft of the nail abutting against the lateral cortex in the femoral canal and distally fixed to the medial femoral condyle by the locking screw in the ring. The position of nail in head/neck corresponds to the compression trabeculae, and it functioned as a load sharing and not a load bearing as other prevailing implant.

RESEARCH/PUBLICATION ON SEN’S NAIL

The Sen’s nail had gained popularity in eastern India during 1970s and 80s, but there is hardly any publication on it. A very few research/thesis work on this nail was done at the Calcutta University level. One example is of Prof. (Dr.) Tapas Chakraburtty (Retd. Professor and Head, Department of Orthopaedics, RKMSP, Kolkata) who did his thesis on Sen’s nail in 1981.[²]

FINAL REMARKS

Sen’s nail was found to be one of the easiest and cheapest ways to address the peritrochanteric fractures in developing countries. The operation takes less time and negligible blood loss and less morbidity because of early mobilisation.

The popularity could not reach to the zenith: firstly because of dearth of followers and trainers in his posterity and secondly because of the development of newer implants and newer technology over the period of time.

Sen’s nail born from the necessity of a chip, less traumatic, and more universally applicable fixation device in the elderly medically compromised patients. The simplicity and pan applicability in the targeted population make us wonder at the ingenuity of our past legend.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Authors’ contributions

SK: He prepared the manuscript by compiling the information gathered by personal communication with coauthors of this article (TC and DKM). He also included the information gathered by himself during his J&J Fellowship whilst visiting RKMSP Hospital in 2010. DKM: He gave inputs (by personal communication) about “Sen’s nail,” as he worked under Dr. Biswajit Sen (innovator of Sen’s nail) as his P.G. student. He edited the entire article for final submission. TC: He gave inputs (by personal communication) about “Sen’s nail,” as he worked under Dr. Biswajit Sen (innovator of Sen’s nail) for long time. He also included the information whilst doing thesis on “Sen’s nail.” He edited the entire article for final submission.