Dissection comes from the Latin word “Dissecare”. It means study of body parts by cutting. It should be made cleanly with a firm and controlled stroke of knife and scissors. Dissection of cadaver is an active learning process by which one can assess the three-dimensional architecture of human body. The first Indian who made dissection is Pandit Madhusudan Gupta with four other doctors in Medical College, Bengal on 10th January 1886. Always try to demonstrate structures as cleanly as possible, by removing fat, connective tissue and small veins. In this book of the dissection methods are presented on regional basis starting from superior extremity—“upper limb”, inferior extremity—“lower limb” abdomen, thorax head and neck and lastly brain. One should have the idea that all gross anatomical structure written in anatomical textbooks are found in dissection but as the time is short and one has to learn more practical anatomy, first minor structures particularly veins which has less importance as it follows arteries should be cut out for visualizing the important structures.
As we are dissecting the dead body the elasticity of skin and tissue are very limited but in living body the structure are very elastic and soft. When you read anatomy always try to learn the subject by inspection (one can see), palpation (feel by palm of hand) of living body and compared their position in dead one.
Instruments Used During Dissection
- Scalpel (Figs 1.1A and B): This are used to make incision and cutting of tough tissues. It consists of changeable blade and handle. Handle should be of standard type, Handle No 4 in suitable for dissection so that it can hold a variety of blades. Blades should have straight back and should be of 3.5 to 4 cm long. Blade No 20 fits to handle No 4 is suitable for all dissection.
- Scissors: Two varieties of scissors are used during dissection (Do not buy a small scissors). Ideal length of scissors are from 15 to 20 cm (Fig. 1.2).
- Sharp pointed scissors: It is more commonly useful where there is finer dissection and have to separate an artery from vein (Fig. 1.3).
- Blunt scissors: This scissors are used to cut anything tough structure like tendon or when you apprehend to damage a structure. In using this scissors blunt head should be placed where you think that there will be damage of structures.
- Forceps: It grips the structures firmly and can lift the tissues and blood vessels so that one can visualize the deeper structures. It is of three varieties (requires during dissection). The length of the forceps should not be less than 10 cm and not more than 20 cm.The three varieties are:
- Nontoothed forceps (Fig. 1.4): More useful during dissection; they are used to hold soft structures. Note that serration of the ends must be fairly large and fit well together. Test its gripping tower by holding a hair of your hand.
- Toothed dissecting forceps (Figs 1.5A and B): They are used to hold skin, tough structure (like deep fascia) during dissection. All forceps must possess grooved handles which makes them comfortable to hold.
- Allis' tissue forceps: The tip of this forcep is provided with interlocking tooth. It is used in anatomy for holding the structure like skin, superficial fascia, rectus sheath and it also act as a retractor during window dissection (Fig. 1.6).
- Rib share: It is a heavy instrument used in anatomy for cutting ribs; when one have to visualize the right or left side of thoracic cavity. But the demerit of this instrument is that cut bony surfaces are not smooth (Fig. 1.7).
- Osteotome: It is an instrument that looks like chisel (use by carpenter) but it cut edge is beveled on both sides. It is used for removal of skull cap during removal of brain from cranial cavity (Fig. 1.8).
- Bone saw: It is used to cut the bones with a regular surface. The bone saw has a fixed or detachable type of blade. It is used in rib cutting, section cutting, etc. (Fig. 1.9).
- Gloves: A pair of gloves is needed. First, the hands are well powdered. The turned up cuff of the left hand glove is held in right hand and the glove is slipped on to the left hand. Similarly, left hand is used for wearing gloves on right hand (Fig. 1.10).
Methods of Embalming of Dead Body
It was first done by the Egyptian for preservation of dead body as mummy. A 6 cm long vertical incision is given in the upper and medial side of thigh and femoral sheath is exposed. The sheath is excised and femoral artery is identified by tube like appearance. About 7 liters of embalming fluid prepared by mixing appropriate amount of formalin (5 liter), glycerin (1 liter), alcohol (1 liter), etc. is put in the injector. The amount may increased if the body is large. A small nick is made in the femoral artery and cannula of the injector introduced (Figs 1.11A and B) so that it points towards the head end and 4 liters of fluids pumped in under 8 kg of pressure. The direction of the cannula is reversed and the rest of the fluid is pumped in opposite direction. The skin over the thigh is stitched. Salt may be applied in the embalming fluid. It will nicely preserve muscle but there is chance of fungus infection of the body, if body remains for prolonged period.
Figs 1.11A and B: Technique of embalming of body (dead). Injector—A machine by which embalming solution is introduced in the dead body
Tricks for Meticulous Dissection
- Good light is required (either good north light form window or artificial light).
- Comfortable stool with adjustable height so that the dissector do not fatigue.
- When you will visualized the dissected part, you will not see the typical color of artery (red), vein (blue) and nerve (yellow) presented in the diagram of a book. In the formalin hardened body you should identified artery which has got a thicker wall than vein (thin walled and sometimes there is blackish blue coloration). Nerve trunk is white thick structure and not easily torn if you pull them by means of forcep. It has cord like feeling as there is no lumen. Muscle tendon is to be differentiated from nerve by their shiny appearance and linked to muscle belly.
- Please note that all bodies looks same and in basic architectures but no two bodies are identical. Minor variations are always present.
- During dissection you will notice that skin varies from region to regions. The skin is relatively thin in front of arm, forearm, perineum and external genitalia, in contrast it is considerably thicker in the region of palm, sole and back.
- Deposition of fat in superficial facia is also variable in different parts. Deposition of fat is more in female than male. See the figure where deposition of fat is more (Figs 1.12A and B).
- Cleaning of muscles: It is covered by epimysium and perimysium. The thickness of epimysium and perimysium varies greatly. Clean the epimysium by scissors. You lift the epimysium by forceps, make a small nick by scissors and extends the incision so that muscles become clean. You can tear it by finger also. Take care during dissection of muscles of face. It is very delicate and soak it with water during dissection. The muscles of this region are pale than any other parts of body.
- Listen student, the dissection depend on climate, time taken to finish it and proper embalming of body. Our country is tropical country there is drying up of structures very quickly. So we shall not cut the whole skin and superficial fascia at a time but to preserve it for demonstration of structure step by step. This will also maintain the freshness of deeper structure as far as possible.
- It is common question of student why there is difference between surgical incision and cadaveric incision. You know that the living body is elastic and so in a small incision we can expose more area due to elasticity and by putting retractor. But the dead body is firm due formalin, so exposure of structure is less and requires large incision.
- Incision should make cautiously so that it does not exceed the thickness of skin.
- Another misconception regarding space (e.g. thenar space, pulp space, triangular and quadrangular space, etc.) is that, it is actually a potential space which is occupied by loose areolar tissue that can be distended during accumulation of pus.
- Always notice that, referred pain from deep fascia is sharply localized.
- During dissection one must always used toothed forceps for holding skin during its removal.
- The scalpel blade should be directed towards the skin otherwise it will include more tissue when you will extends the incision. Hold the scalpel in pen holding fashion.
- Always use scalpel handle (without blade) or finger, during separation of cleavage lines between muscles (in limbs). If one use sharp instrument muscle will be lacerated (damaged) and artificial cleavage may mislead you.
- Clean the structures (which is to be identified) by removing fat, connective tissue and small veins.
- Care should be taken to separate small artery from vein by scissors (Fig. 1.13).
Fig. 1.13: Separation of vein from artery by scissors (closed scissors are inserted between artery and vein and then opened it)
DIFFERENCE BETWEEN WINDOW DISSECTION AND IDENTIFICATION
We can have the idea how surgical procedure can be done through limited incision
Level at which the structures lies (superficial or deep)
It is suitable for our climate as it maintain the freshness of deeper structures
As there is advancement of minimum invasive surgery like lap-chole, laparoscopic ligation, etc.— the importance of window dissection gradually become more and more usefull
Better exposure of structures for detailed study
Study of deeper structures requires removal of superficial structures for proper visualization and know the proper extension of deeper structure
It will cause drying up of structures very soon or there is maggot infestation if it is not kept properly is the vat (large container)
Both methods are necessary. Please do the window dissection first and then go for identifications of structures. It will minimize cadaver westage and the labor of human resources
For maximum utilization of body, and minimum labor we do the dissection of front first then turned the body with face below and do the dissection of back (in case of limbs).
POSITIONING OF BODY AND TERMINOLOGY OF BODY REGIONS
Positioning (Body Posture) (Figs 1.14A to E)
Fundamental position: It is like anatomical position. Here palm is on the side of the trunk which is the usual position in our body. All the patients are examined in this position.
Anatomical position: It is the position in which a person is standing erect, with eyes looking towards horizon, arm is by the side of the trunk, palm faces forwards.
Supine position: The subject is lying on the back with face up.
Prone position: The subject is lying with face down and belly on the table.
Lateral position: Position in which the side of the subject is adjacent to the table.
Lithotomy position: The subject is lying in supine position with flexed hip and knee, and the thigh is widely separated. It is useful in dissection of perineum and during delivery.
Anatomical Terms (Figs 1.15A to E)
- Superior or cephalic—towards the head or upper part of a structure, e.g. the head is superior to the neck.
- Inferior or caudal—away from the head. Navel is inferior to the chest.
- Anterior or ventral—towards the front part of the body.
- Posterior or dorsal—towards the back part of the body.
- Medial—towards the middle part of the body.
- Proximal—closer to the origin (closest to the trunk).
- Distal— away from the origin (away from trunk).
- Superficial—towards the body surface (muscles are deep) but skin is superficial.
- Per—through, e.g. per-rectal examination (P/R exam) through rectum.
REGIONAL TERMS FOR SPECIFIC BODY AREAS (FIG. 1.16)
- Frontal (Forehead)
- Orbital (Eye)
- Nasal (Nose)
- Buccal (Cheek)
- Oral (Mouth)
- Mental (Chin)
- Cervical (Neck)
- Acromial (Point of shoulder)
- Axillary (Armpit)
- Sternal (Breast bone)
- Thoracic (Chest)
- Mammary (Breast)
- Abdominal (Belly)
- Umbilical (Navel)
- Pelvic (Pelvis)
- Inguinal (Groin)
- Coxal (hip)
- Femoral (Thigh)
- Patellar (Anterior knee)
- Peroneal (Side of leg)
- Crural (Leg)
- Tarsal (Ankle)
- Digital (Toes)
- Hallux (Great toe)
- Cephalic (Head)
- Otic (Ear)
- Occipital (Back of head)
- Vertebral (Spinal column)
- Scapular (Shoulder blade)
- Brachial (Arm)
- Antebrachial (Forearm)
- Lumbar (Loin)
- Sacral (Between hips)
- Gluteal (Buttock)
- Popliteal (Back of knee)
- Sural (Calf)
- Calcaneal (Heel)
- Plantar (Sole)