Anatomical basis for surgical routes of approach Flashcards
What factors/ structures need to be considered when planning/ taking a surgical route of approach?
- Healing time
- amount of tissue damage vs suitable amount of access
- avoid nerves and blood vessels
- surface anatomy –> organs
- what layers will you cut through
Langer’s lines:
What are they?
What are they determined by?
why are they useful surgically?
what sort of incision enables adequate exposure during surgery?
The skin possesses lines of tension/ cleavage (langer’s) which help guide the orientation of surgical incisions
Langers lines are determined by the direction of travel of collagen fibres in the skin
Incisions along langer’s lines can heal better + lead to minimal scarring
Z-plasty incisions (used to access flexor tendons) enable adequate exposure whilst enabling closer alignment with the skin tension lines
if you caused scar tissue on the flexor surface of palms/ digits –> fixed flexion of digits
What is important for skin incisions during surgery?
Skin incisions must provide adequate access to safely perform an operation under optimal condition + there should be an option to increase access
(example shown approach to access radius, moving muscles to access)
Why is surface anatomy important in surgical approach?
Surface anatomy guides the safe + appropriate placement of incisions + anaesthetic in the hand for example:
Z plasty incision runs on the palmar surface of the hand, avoiding the NV structures that run medially and laterally on the digits.
What are at risk at the primary incision site?
- Cutaneous and superficially positioned nerves are at risk at the primary incision site + in biopsy procedures
- E.g. the accessory nerve is very superficial in position + so neck surgery presents high risk of damage
- Marginal mandibular nerve (running over submandibular gland) -> motor nerve branch of CNVII)
- lose supply corners of mouth will be permanently drawn up on one side
- Some cutaenous nerves are unavoidably damaged during certain surgical approaches
- saphenous nerve branch that innervates skin over lateral side of knee –> will need to be cut during knee surgery (arthroplasty) –> leads to tingling/ paraesthesia or complete sensory loss on lateral side of knee
What do fascial planes provide?
what other structures can also provide this?
Fascial planes can provide avascular and aneural routes of approach through complex regions
e.g. see neck dissection -> EJV avoided by following fascial planes
Intermuscular septa (that separate muscular compartments, attach at the bone) therefore can also provide avascular routes right down to the bone.
Muscle fibre direction:
What is the importance of minimising tissue damage?
How can you minimise tissue damage?
What are the anterior abdominal wall muscles?
How do fibre directions change as you go through muscle walls?
Minimising tissue damage is ideal –> reduces time in hospital and time in recovery.
To minimise tissue damage muscles can be split in the direction of travel of their fibres
Anterior abdominal wall muscles –> external oblique, internal oblique, transversus abdominus
Neurovascular plane lies between the internal oblique and transversus abdominus layers. Damage to a nerve paralyses the muscle distal to the nerve damage –> muscle weakness and increased risk of herniation
Fibre directions change as you go through muscle layers. Do not need to incise but peel the muscle fibres apart with retractors + after procedure the muscle fibres come back together. Since they’re arranged at different angles the chances of herniation is minimal. Must take care to avoid the incision or compression of nerves –> relies on knowledge of the position of the neurovascular plane
Damage to nerves leads to paralysis of muscle distal to point of damage –> at risk of herniation + hernia formation.
What are vascular watershed points?
What can this lead to?
Vascular watershed points –> regions of dual blood supply from the most distal branches of two arteries e.g. splenic flexure of large intestine
midgut/ hindgut boundary 2/3 across the transverse colon, midgut supplied by SMA, hindgut supplied by IMA
border at 2/3 across transverse colon = vascular watershed + may not be as good blood supply to other parts of the intestine as the blood vessels get smaller as they approach it.
If you need to operate on a watershed region and you need to reanastamose the ends of the bowel - not done in the watershed, take much wider margins so you can reanastomose the vascular tissue.
Reduces the risk of infarction, therefore better healing.
Why is vascular watershed region avoiding when anastomosing the large bowel?
Vascular watershed region avoided when anastomosing the large bowel to make wider margins to re-anastomose vascular tissue, risk of infarction is less.
What is the allantois/ urachus?
What vitellointestinal duct?
What can go wrong with these structures?
On the picture below: Two bits of tissue that project into the umbilicus
–> Top one = vitellointestinal duct
Bottom one –> = Allantois which becomes the urachus in adults–> forms the umbilical arteries and vein
Urachus –> the urachus is a duct extending from yolk sac to apex of the bladder, yolk sac forms the allantois which becomes the urachus. During development the lumen of the urachus closes, adult remnant is the median umbilical ligament.
If the Urachus fails to close –> can develop urachal cysts, urachal sinus (abnormal connection between bladder and belly button, discharge) or patent urachus (urachal fistula) or can get a vesicourachal diverticulum (bladder protrudes from umbiicus). If cyst is being removed, surgeon has to remove all of the tissue or recurrence will happen.
Vitelline duct –> connects yolk sac to midgut, closes during week 7. If vitelline duct fails to close then vitelline fistula where meconium discharge from umbilicus. Or in the adult you can get a cyst, must remove entire tissue or the cyst can reoccur. Or meckels diverticulum (remnant of the vitellointestinal duct) (Right hand side of picture).
Knowledge of the origin and movement of a tissues neurovascular supply helps define avascular and aneural surgical approaches
what is the development of the gut tube and therefore the arrangement of the blood supply?
Knowledge of the origin and movement of a tissue’s neurovascular supply helps define avascular and aneural surgical approaches.
Development of gut tube:
- Gut tube derived from endoderm, running from prechordal plate (mouth) to cloacal membrane (anus)
- at 6 weeks midgut elongates to form a ventral U shaped midgut intestinal loop
- Midgut loop communicates with yolk sac via vitelline duct or yolk stalk and travels within umbilicus
- As a result of rapidly growing liver/ kidneys and gut the the abominal cavity is temporarily too small to contain the midgut, it projects into the umbilical cord —> physiological umbilical herniation.
- 3 blood supplies form off the aorta- coeliac trunk, SMA, IMA
- Midgut undergoes rapid elongation and forms a hairpin loop around the mesenteric artery, midgut then rotates around the superior mesenteric artery anticlockwise 90 degrees in umbilicus, and then a further 180 degrees as elongated intestines fall back in abdomen (total 270 degrees anticlockwise).
- Rotation places cecum in R lower quadrant, ascending and descending colon contact dorsal body wall upon return and eventually fuse, becoming secondarily retroperitoneal.
What do we know about the blood supply to the gut and therfore how does this help guide which surgical plane of approach to use when resecting the colon?
We know blood supply to the Gut is from the midline (off aorta), runs laterally towards the colon. Tells us surgically can travel behind the colon, which puts us in the avascular plane. Used in resection of the colon.
White line of Toldt
In picture –> caecum at the top, and at the botton is the posterior abdominal wall, structure across = white line of toldt.
Cut behind that, enter the avascular and aneural plane –> safe for resection of the colon.
What is the white line of toldt and retrocolic plane?
Why is this useful in surgical approaches?
The white line of toldt represents the lateral fusion line between the colon and retroperitoneum. The retrocolic plane is behind the ascending and descending colon.
regardless of dissection approach during a laparoscopic colectomy, ultimate goal is to separate colon and its mesentery away from retroperitoneal structures and develop the colon as a midline structure, if dissection started medial to white line of toldt, allows entry into appropriate plane between colon mesentery and retroperitoneum, avoids injury to retroperitoneal structures and unwanted bleeding.
Why are avascular planes useful?
which organs are segmented? Why is this knowledge useful?
Avascular planes can be used to approach multiple organs –> e.g. using the retroperitoneal plane behind the descending colon –> can ascend in this plane to access the kidney via one port.
e.g. live renal donation can now be done through a single endoscopic port using an avascular plane behind the colon.
Segmented organs –> consist of functionally independent segments/units: lungs, liver, kidneys, spleen. Exploited surgically e.g. liver remove cerain segments, except in spleen - too delicate.
What is the use of a median sternotomy?
Midline/ median sternotomy provides very good access to mediastinal structures particularly the heart and great vessels.
Mostly causes bone damage. By approaching midline avoid the NV bundle associated with the ribs. Avoids intercostal muscles, internal thoracic artery and vein.
Provides very good mediastinal access.
Tissue damage to the skin, superficial tissues and bone, pain post procedure as bone moves with breathing, have to wire sternum back together for stability.
What is the name of this incision?
Would we be happy with this incision?
How would you landmark this incision?
Thoracostomy –> One shown is too low. High risk to the liver and the diaphragm, need to put insertion at the safe zone.
Landmarking: See on the picture below –> The anterior axillary fold, the posterior axillary fold, the mid-axillary line. Old “triangle of safety” was between the anterior and posterior axillary fold and the line drawn off the nipple. Poor landmarking as the nipple is highly variable structure positionally, and risk to the long thoracic nerve that innervates serratus anterior –> winging of the scapula.
Now –> Count ribs off the sternal angle (costal cartilage 2), count down two ribs, procedure is done in the 4th intercostal space. Revised between anterior axillary fold and the midaxillary line.
What if wide/ fast access is needed to the lungs/ heart –> what incision would you use?
Safe to approach from 4th or 5th intercostal space (4th preferred avoids other structures) –> cut from midaxillary line all the way to the costal cartilage at the anterior aspect.
Long term problems post this incision?
Damage to the neurovascular supply to the intercostal muscles –> flaccid paralysis of the intercostal muscles leading to paradoxical chest movement during breathing
+ PAIN –> often long term and severe
What is a clamshell thoracotomy used for?
What is wrong with the incision shown?
Clamshell thoracotomy used for emergency access to the mediastinum.
Straight approach through the thorax –> will cut directly through the ribs, and in the midline –> could damage the liver. Incision should be swallow shaped and follow the intercostal spaces. Can gain access to the thorax in 45 s
Name the incisions shown”
7
9
12
7 - subcostal
9 - midline (cuts linea alba - problem avascular –> poor healing)
12 - suprapubic (gain uterine access)
What needs to be considered during access to the abdominal wall?
What is Lee Huang point?
What is palmers point?
Neurovascular supply to the anterior abdo wall needs to be considered during incision and trochar insertion (endoscopic procedures).
Particularly –> superior and inferior epigastric arteries. Inferior epigastric artery runs through the rectus abdominus rectus sheath –> leads to rectus sheath haematoma –> cause of abdominal pain
Lee huang point = between xiphoid and the umbilicus
Palmers point = 3cm below the costal margin on the midclavicular plane
Label the structures shown
What are the layers cut through in this approach?
Tensor fascia lata and iliotibial tract, intermuscular septum –> follow to the femur
Access the shafts of long bones (femur and tibia)
How is the femoral shaft approached?
Would not approach at the femoral triangle, and would not approach posteriorly –> sciatic nerve which splits into tibial and the common fibular nerve.
Skin, sub cut fat, iliotibial band, vastus lateralis
Access to the femur:
what approaches should be avoided and why?
What approach would you take and what layers will be cut through?
Would not approach anteriorly at the femoral triangle, and would not approach posteriorly –> sciatic nerve which splits into tibial and the common fibular nerve.
Approach laterally:
Skin, sub cut fat, iliotibial band, vastus lateralis
What structures can provide a relatively simple route of approach to the bones of the lower limb?
Intermuscular septa can provide a relatively simple route of approach
How is the knee joint approched?
What structures are cut through on the correct approach?
Knee is not approached from the back -> as it is the popliteal fossa that contains a number of important structures (popliteal artery, popliteal vein, sciatic nerve splitting into tibial nerve and common peroneal/ common fibular nerve.)
Knee is approached from the front, an incision on the medial side of the knee (anteromedial), patella is pushed to one side.
Three layers to medial knee:
Layer 1 = sartorius, gracilis and semitendinosus )split sartorius from vastus medialis)
Inbetween layer 1 and 2 is deep fascial plane
Layer 2 = semimembranosus, superficial MCL, posterior oblique ligament, medial patellofemoral ligament
Layer 3 = deep MCL, capsule, coronary ligament
What is an arthroscopic procedure
What are the approaches?
Arthroscopic procedure = minimally invasive procedure to gain access to the knee joint by inserting an endoscope through various skin incisions in the knee.
AL portal (lateral approach)
AM portal (medial approach)
PM (posteromedial appraoch)
How is the hip joint approached and why?
What are neurovascular structures at risk when using this approach of the hip?
Avoiding the anterior approach again due to femoral triangle structures, and avoiding purely posterior approaches due to sciatic nerve. Instead there are two approaches.
Posterolateral approach –> cuts through skin subcut fat, gluteus maximus, (may go through medius) then will have to go through the lateral rotators of the hip.
Neurovasculature at risk of damage –> sciatic nerve located along posterior surface of quadratus femoris muscle (lateral rotator), Inferior gluteal nerve (innervates the gluteus maximus) and artery (inferior gluteal artery leaves below piriformis) , superior gluteal artery and nerve, runs over piriformis between glut medius and minimus. Femoral vessels are at risk of compression (not sure why…) - protect anterior acetabulum..
Apart from the posterolateral approach to the hip what is the other approach that can be taken?
What layers do you go through?
What nerves are at risk of damage in this procedure?
Anterior (smith-peterson) approach to the hip
Again avoids the femoral triangle.
Identify gap between sartorius and tensor fasciae latae, disect sub cut fat, incise medial tensor fascia latae, then deep plane of dissection, go between rectus femoris and gluteus medius, retract rectus femoris and iliopsoas medially, gluteus medius laterally –> exposes hip capsule.
Nerves at risk –> lateral cutaneous nerve of the thigh (damage leads to meralgia paraesthetica, tingling, burning and pain on the outer side of the thigh). Femoral nerve also at risk, should be protected by staying lateral to the sartorius muscle, Ascending branch of lateral femoral circumflex artery also at risk (inbetween tensor fasciae latae and sartorius).
Access to the shoulder - what approach is taken and why?
What two bony landmarks help map this approach?
Lateral - deltoid splitting approach is taken to the shoulder –> avoids the axilla with brachial plexus, axillary artery etc…
Lateral approach marked by the acromion and the coracoid process, cut made down from the coracoid process, muscle layers inbetween are deltoid and pec major. On deltoid there are tendinous intersections, that structure is cut, the muscle is opening, and this allows access to the shoulder. See underneath the coracobrachialis - forms a simple guide remain lateral to this. Medially is dangerous due to proximity to the brachial plexus
What are these structures shown in the deep dissection of the anterior shoulder?
Structures shown –> R arrow points towards coracobrachialis tendon, attaching at the coracoid process. L arrow points towards the tendon of the long head of the biceps muscle (attaches at glenoid)
Deeper dissection of the shoulder –> what tendon is shown, and why is a stay stich places in the muscle tendon before it is cut from its attachment?
The subscapularis tendon is shown, a stay stich is placed within the muscle to prevent losing the muscle once it is cut (as the muscle will retract without tendinous insertion).
What nerve runs around the surgical neck of the humerus?
The axillary nerve runs in the surgical neck of the humerus
5-7cm from the acromion
It is at risk even during injections!
