Latest / Deep Dive Ortho — Orthopaedic Surgery, AI & Digital Health Podcast. / Hand anatomy and function

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Hand anatomy and function · Deep Dive Ortho — Orthopaedic Surgery, AI & Digital Health Podcast.

• 0:00
  Welcome to the Deep Dive. Today we're diving
• 0:02
  into something really intricate, the world of
• 0:04
  surgical approaches to the hand, wrist, and forearm.
• 0:07
  Yeah, it's an area packed with tiny vital structures,
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  really fascinating stuff. Absolutely. And for
• 0:14
  you listening, if you want to grasp the complexities
• 0:16
  here without getting totally bogged down in medical
• 0:18
  speak, well, that's our goal today. Exactly.
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  We're basing this on a couple of key sources.
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  One's a very detailed medical text on the anatomy
• 0:26
  and surgical technique, sort of the surgeon's
• 0:28
  map, you could say. OK. And the other is a chapter
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  focusing specifically on anesthesia for these
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  upper limb surgeries. which is, you know, just
• 0:37
  as crucial. Right. So the mission today. Basically
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  to pull out the most critical anatomical ideas,
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  the things surgeons absolutely need to know for
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  safe procedures in this very delicate zone, and
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  also to touch on how anesthesia makes it all
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  work for the patient. OK, let's get into it.
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  First up, something that seems obvious, but is
• 0:58
  fundamental, anatomical knowledge. Our source
• 1:01
  really hammers this home, doesn't it? Yeah. It
• 1:04
  really does. It's not just about knowing names.
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  It's about having this like 3D picture in your
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  head of how everything fits and works together.
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  It's paramount for safe dissection. And there's
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  this concept they highlight inner nervous planes.
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  What's that about? Ah, yes. Think of them as...
• 1:20
  Well, natural corridors, they're the spaces between
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  muscle groups that happen to be supplied by different
• 1:26
  nerves. OK, so like a seam. Exactly, like a seam
• 1:28
  in the fabric. By going through these seams,
• 1:31
  surgeons can get to deeper structures, bones,
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  joints, you name it, without cutting through
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  or damaging the nerves supplying the muscles
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  they're moving aside. Which avoids causing weakness
• 1:40
  or paralysis later on. Precisely. Avoiding muscle
• 1:43
  denervation is huge. So finding and using these
• 1:47
  planes, it's a core principle for minimizing
• 1:49
  harm. during extensive exposure. Makes total
• 1:52
  sense. It's like taking the path of least resistance,
• 1:54
  but for nerves. And this whole area, hand, wrist,
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  forearm, it's uniquely challenging because everything's
• 2:00
  so crowded, right? Oh, absolutely. You've got...
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  muscles, tendons gliding smoothly, vital blood
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  vessels, and all those nerves controlling movement
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  and feeling all packed into a really tight space.
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  It's a delicate balance. A small mistake could
• 2:15
  have big consequences. Definitely. That's why
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  the detailed knowledge is so vital. So, to manage
• 2:20
  this complexity, the anatomy is often discussed
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  in terms of compartments. Our source mentions
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  this for both the hand and forearm. Yeah, thinking
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  in compartments is really helpful. It gives structure.
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  In the hand, for example, you've got the thonara
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  compartment, that fleshy bit at the base of your
• 2:35
  thumb. Right, thumb muscles. Mostly median nerve
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  territory. Then the hypothenar on the pinky side,
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  mostly ulnar nerve. You have the interosseous
• 2:44
  muscles between the hand bones. Also ulnar nerve,
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  mostly. Largely, yes. And then the famous carpal
• 2:50
  tunnel. critical channel for the median nerve
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  and tendons heading into the hand. Thinking about
• 2:55
  these zones helps surgeons plan their approach.
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  And our source goes into the specific muscles,
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  their attachments, their nerve supply within
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  each compartment. We're just skimming the surface,
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  but it shows the detail needed. It really does.
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  And similarly, in the forearm, you have compartments
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  too. Superficial volar that's palm facing. Like
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  the wrist flexors? Yeah, things like pronator
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  teres, flexor carpe radialis, mostly median nerve
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  again. Then there's a deep volar compartment
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  and a dorsal compartment on the back. Knowing
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  which compartment you're in tells you what structures
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  to expect. It's like a roadmap. OK, so moving
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  from the map, the anatomy to the actual journey,
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  the surgery. The source talks about principles
• 3:36
  of surgical management. Planning seems key. Non
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  -negotiable. The text stresses that every single
• 3:43
  approach needs that solid understanding of anatomy
• 3:46
  surface and deeps, plus those inner nervous planes
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  we talked about, and of course, good surgical
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  technique. And it's not just knowing the steps
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  right. There's a lot of prep work. A huge amount.
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  Making sure you have all the right instruments,
• 3:57
  the right sutures, imaging available if needed.
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  If you're putting in plates or screws, they have
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  to be ready. Exactly, using x -rays or scans
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  to plan implant sizes and positions beforehand.
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  The whole team reviews the anatomy, the approach,
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  the procedure itself, and even discusses alternatives,
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  what if Plan A doesn't work? And the OR setup.
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  Seems like small details matter. They really
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  do. Patient positioning is usually supine, lying
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  on their back with the arm out on a special hand
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  table. That table needs to be rock solid. For
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  precision. Absolutely. And the surgeon needs
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  a stable stool, good lighting. really good lighting,
• 4:34
  angled properly to avoid shadows. It all contributes.
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  And the tourniquet. That's standard for a bloodless
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  field. Almost always in hand and wrist surgery,
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  yes. A pneumatic tourniquet on the upper arm.
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  It gives you that clear view which is just essential
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  when you're working around nerves and tiny vessels
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  like working on a delicate machine. Right. Now
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  let's talk incisions. Making the cut in the hands
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  specifically. Are there general rules? There
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  are. The source says you can technically make
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  an incision almost anywhere, but you have to
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  respect certain principles for good healing and
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  function. Avoid areas that stay damp, like deep
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  creases sometimes, and plan so the skin edges
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  come together nicely without tension. And they
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  mark the incision beforehand, with a sterile
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  marker. Always. Standard practice lets you visualize
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  it, check placement, make sure you leave enough
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  skin between cuts if you need multiple incisions.
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  It's a guide. Okay, and differences between palm
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  side volar and Back of hand dorsal incisions.
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  Yeah, that's important on the palm The subcutaneous
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  tissue can be thin and incisions right in the
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  deep creases might not heal quite as well And
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  a big don't is making straight incisions across
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  the flexion creases. Why is that? scar contracture.
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  Exactly. It can lead to tight scars that limit
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  bending later on. The skin on the back of the
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  hand is generally looser, more mobile, so sometimes
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  you can get away with a slightly smaller incision
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  there. And the shape of the incision can vary
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  too, like zigzags. Definitely. Zigzag incisions
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  are common on the volar side of fingers. They
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  break up the line across the creases. On the
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  back, you might see straight lines or gentle
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  curves. Medaxial incisions along the side of
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  the finger need extra care because of the neurovascular
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  bundles running there. Okay, let's get more specific.
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  Approaching the finger joints, the interphalangel
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  joints. Right, the hinge joints in your fingers.
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  Surgeons often use dorsal incisions straight,
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  S -shaped, maybe chevron. A common way in is
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  from the side, carefully lifting and retracting
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  the lateral bands of the extensor tendon mechanism.
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  Any specific precautions depending on which joint?
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  DIP versus PIP. Yes. At the DIP joint near the
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  nail, you have to be super careful of the geminal
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  matrix where the nail grows from. It's right
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  near the tendon insertion. At the PIP joint,
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  the middle one, the extensor mechanism is right
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  there under the skin. No inner nervous plane
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  there. Correct. For more exposure at the PIP,
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  they might carefully release and repair those
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  lateral bands, or even create a V -shaped flap
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  in the extensor tendon itself, which gets meticulously
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  repaired. But the absolute key is presuming the
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  central slip of that extensor tendon. That's
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  vital for straightening the middle part of the
• 7:08
  finger. Got it. What about the knuckles where
• 7:11
  fingers meet the hand, the MCP joints? Metacarpal
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  phalangeal joints, yeah. Usually a straight dorsal
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  incision over the knuckle, maybe transverse if
• 7:20
  doing multiple fingers. Again, no real inner
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  nervous plane extensor mechanism is right there.
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  Need to watch for little sensory nerve branches.
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  And getting into the joint itself, different
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  options. Several ways. You can retract the sagittal
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  band, that little sling holding the tendon centered.
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  or carefully split the extensor tendon lengthwise,
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  but you have to be careful not to go too far
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  down and damage that crucial central slip insertion
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  at the PIP joint. You mentioned that central
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  slip is key. It really is. Another option is
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  incising along the ulnar side sagittal band,
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  but they try to avoid releasing the radial one
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  on the thumb side to prevent the tendon from
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  slipping off track. OK, how about accessing the
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  long bones in the hand, the metacarpals? You
• 8:00
  feel for the bone, identify the extensor tendons
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  running over it, then usually a straight dorsal
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  incision right over that bone, sometimes between
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  two metacarpals if needed. Still no inner nervous
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  plane. Not really a true one there. So it's about
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  carefully identifying and protecting those extensor
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  tendons and the little cross connections between
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  them, the juncture. Then you make an incision
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  in the periosteum, the bone's outer layer, and
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  gently lift the interosseous muscles off the
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  bone. Superior steel elevation. Let's move to
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  the wrist now. Carpal tunnel, everyone's heard
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  of that. How does it approach? Right. So the
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  carpal tunnel itself, narrow passage, median
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  nerve, nine tendons. Roof is the thick transverse
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  carpal ligament. Floor and sides are the carpal
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  bones. Extends up to the wrist crease. Lamp marks.
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  Surgeons use the interthinar depression, that
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  little dip near the thumb base. They can feel
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  the pisiform bone, maybe the hook of the hemat.
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  And there's Kaplan's cardinal line, an imaginary
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  line helping locate structures. And the incision
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  has to be super careful because of the median
• 9:00
  nerve. Extremely careful, usually centered in
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  that interthinar depression, aiming towards the
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  space between the third and fourth fingers. This
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  helps avoid the palmar cutaneous branches of
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  both the median and ulnar nerves. That's essentially
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  the inner nervous plane there. You cut through
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  fat, the superficial palmar fascia, then carefully
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  divide the transverse carpal ligament itself,
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  always watching for the median nerve right underneath,
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  and especially its recurrent motor branch to
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  the thumb muscles, which can sometimes have unusual
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  anatomy. And there's a sign when you're fully
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  released? Yeah. Distally, you look for this little
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  pad of fat, the sentinel fat pad. that confirms
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  you've cut the ligament all the way. What about
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  the canalogion, the other tunnel on the pinky
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  side? Right, ulnar nerve and artery pass through
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  there. Borders involve the volar carpal ligament,
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  transverse carpal ligament, pisiform bone, hook
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  of hamate. You palpate the pisiform, try to find
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  the hook. Tricky to feel sometimes. Can be. The
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  incision is usually zigzag or curved between
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  those points, extending up the forearm a bit,
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  but again, avoiding crossing the wrist crease
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  straight on. You find the flexor carpi ulnaris
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  tendon. Move it aside gently. The ulnar, nerve,
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  and artery are right there. And then release
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  the ligament. Release the volar carpal ligament
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  to decompress the nerve and artery. Important
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  to remember, the ulnar nerve splits here into
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  motor and sensory branches, and the motor branch
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  often ducks under a little fibrous arch. Anatomy
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  varies a lot here, the source notes. OK, moving
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  up the forearm. The radius thumb side bone. Yeah.
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  Volar approach first from the palm side. Right.
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  Key landmarks. Feel for the flexor carpe radialis
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  tendon, the brachioradialis muscle belly, biceps
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  tendon higher up, radial artery pulse, the inner
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  nervous plane changes a bit. Distally, it's between
• 10:44
  flexor carpe radialis, median nerve. and brachioradialis,
• 10:48
  radial nerve. Ah, you're up. Proximally, it's
• 10:50
  between pronator teres, median nerve, and brachioradialis,
• 10:54
  radial nerve. The incision is usually just above
• 10:56
  the wrist crease, thumb side of the FCR tendon
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  going upwards. You dissect down between FCR and
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  brachioradialis. Watch out for it. Radial artery,
• 11:04
  definitely. Median nerve is a bit deeper. And
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  the superficial radial sensory nerve can be in
• 11:09
  the way lower down. Sometimes they go through
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  the FCR sheath instead. To get to the bone itself,
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  you often have to lift overlying muscles like
• 11:16
  pronator quadratus or flexor pollicis longus
• 11:18
  off the radius. Now the dorsal approach to the
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  radius from the back. OK. Land works here. Lister's
• 11:24
  tubercle on the wrist end of the razeus, lateral
• 11:26
  epicondyle at the elbow, and that group of muscles
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  called the mobile wad of three. Incision runs
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  from Lister's tubercle towards the lateral epicondyle
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  along the inner edge of that mobile wad. Inner
• 11:37
  nervous plane here. Can it shifts? Distally,
• 11:39
  it's between extensor carpi radialis brevis.
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  ECRB, often radial or pin supplied, and extensor
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  pollicis longus, EPL, PM supplied. Proximally,
• 11:50
  it's between ECRB, radial nerve, and extensor
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  digitorum communus, EDC, PI supplied, the finger
• 11:56
  expansion. Duct dissection. You open the extensor
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  retinaculum over the EPL tendon, move tendons
• 12:01
  aside. Higher up, you detach muscles like abductor
• 12:04
  pollicis longus. The really crucial structure
• 12:07
  in the upper third is the supinator muscle. What
• 12:09
  is that? Because the posterior interosseous nerve,
• 12:12
  PI, a branch of the radial actually runs through
• 12:15
  the supinator. You absolutely have to find and
• 12:18
  protect that nerve before you release the muscle
• 12:20
  from the bone to see the radius underneath. Very
• 12:23
  important point. Okay, finally, the ulna. Pinky
• 12:25
  side bone. Accessing the ulna is often a bit
• 12:27
  more straightforward because much of its border
• 12:29
  is right under the skin subcutaneous. You identify
• 12:32
  the head and styloid at the wrist, feel that
• 12:35
  border along the forearm up to the ola crana
• 12:37
  on the elbow point. Incision follows that border.
• 12:40
  Inner nervous plane for the ulna. Distally, it's
• 12:43
  between flexor carpial nervous, FCU ulnar nerve,
• 12:47
  and extensor carpial nervous, ECU, PIN supplied.
• 12:51
  Proximally near the elbow, it's between FCU ulnar
• 12:54
  nerve and the inconeus muscle radial nerve. You
• 12:57
  also have to be mindful of the dorsal sensory
• 12:59
  branch of the ulnar nerve wrapping around. And
• 13:01
  then lift the muscles. Gently elevate the muscles
• 13:04
  off the bone superior stele. Protect the ulnar
• 13:07
  artery and nerve, especially near the wrist.
• 13:09
  Proximally, you note the triceps insertion in
• 13:11
  the path of the ulnar nerve going behind the
• 13:13
  medial epicondyle, the funny bone spot. Wow,
• 13:16
  that covers a huge amount of surgical anatomy.
• 13:19
  So detailed. Now, let's shift gears to our other
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  sorts anesthesia, equally vital. Right, absolutely
• 13:25
  critical. And the landscape has changed, you
• 13:27
  know. More outpatient surgery, so managing pain
• 13:30
  after the patient goes home is a huge focus.
• 13:33
  And regional anesthesia nerve blocks plays a
• 13:35
  big role. I'm Massive Roll. Blocking the specific
• 13:38
  nerve supplying the surgical area often gives
• 13:40
  much better pain relief than general anesthesia
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  alone. Plus, less nausea, less vomiting, patients
• 13:46
  generally feel better and recover faster. And
• 13:48
  the blocks can last longer now, even continuous
• 13:51
  relief. Exactly. Long -acting local anesthetics
• 13:54
  help. But for really sustained relief, they can
• 13:56
  place a tiny catheter near the nerve. An indwelling
• 13:59
  catheter. Right. And a small pump infuses local
• 14:02
  anesthetic continuously, sometimes for days,
• 14:04
  even at home. This bridges that gap when a single
• 14:07
  shot block would wear off, which can be a really
• 14:09
  rough period pain -wise. So how do they decide?
• 14:12
  General anesthesia, regional, or both? What goes
• 14:15
  into that choice? Several things. How long is
• 14:18
  the surgery? Very long ones might favor general
• 14:21
  for patient comfort. Does the surgeon need to
• 14:23
  check nerve function right away? A block would
• 14:26
  interfere with that initially. Equation factors
• 14:27
  too? Of course. Patients' overall health, anxiety
• 14:31
  levels, any specific medical conditions like
• 14:34
  lung problems if you're considering certain neck
• 14:36
  blocks, and patient preference, naturally. But
• 14:40
  regional seems to have a lot going for it based
• 14:42
  on our source. It really does. Potential benefits
• 14:44
  include smoother or r -flow blocks can often
• 14:47
  be placed beforehand. Easier management for patients
• 14:50
  with certain conditions. That combo of anesthesia
• 14:53
  and post -op cane control from one technique.
• 14:56
  Less nausea, quicker recovery, maybe even less
• 14:58
  post -op confusion or cognitive issues, especially
• 15:01
  in older patients. In different blocks for different
• 15:03
  areas. Yep. Shoulder surgery often uses interscaling
• 15:06
  blocks near the neck. Elbow might be interscaling,
• 15:09
  supraclavicular, or infraclavicular below the
• 15:12
  collarbone. Down in the forearm and hand, you
• 15:14
  might use infraclavicular, axillary in the armpit,
• 15:16
  or even IV regional for shorter things. IV regional.
• 15:20
  Yeah, beer block. Inject anesthetic into an arm
• 15:23
  vein while a tourniquet keeps it in the limb.
• 15:25
  Good for shorter procedures. But regional isn't
• 15:28
  always an option, is it? Contraindications. Right.
• 15:31
  Definite no -go's include acute nerve injury
• 15:33
  in that limb, progressive neuropathy, infection
• 15:36
  right where you'd stick the needle, patient refusal,
• 15:39
  or serious bleeding problems. Then there are
• 15:42
  relative ones, maybe stable nerve issues, severe
• 15:45
  lung disease for high blocks, active infections
• 15:48
  elsewhere. And managing pain isn't just about
• 15:50
  the block, is it? This idea of preemptive and
• 15:53
  multimodal analgesia. Good point. Preemptive
• 15:56
  means starting pain meds before the pain really
• 15:58
  kicks in, even before surgery sometimes. Multimodal
• 16:02
  means using different types of pain relief together.
• 16:05
  Like combining things. Exactly. Maybe an NSA
• 16:07
  WEI plus acetaminophen, maybe something like
• 16:10
  gabapentin for nerve pain alongside the regional
• 16:13
  block. The idea is to attack pain from multiple
• 16:16
  angles, often meaning you need lower doses of
• 16:18
  each drug, reducing side effects, especially
• 16:20
  from opioids if they're needed at all. And like
• 16:23
  with surgery, consent for anesthesia Absolutely.
• 16:26
  The anesthesiologist has to explain the options
• 16:28
  general, regional, the specific block, along
• 16:31
  with the risks and benefits of each. It's a shared
• 16:34
  decision informed by the patient's choice and
• 16:37
  the medical team's recommendation for the safest
• 16:39
  outcome. Finally, let's touch on complications.
• 16:41
  Both general and regional have potential risks,
• 16:44
  right? It's not risk -free either way. No medical
• 16:46
  procedure is entirely risk -free. General anesthesia
• 16:49
  can have post -op nausea, urinary retention,
• 16:53
  rarely things like corneal abrasion or nerve
• 16:55
  injuries from positioning. Interestingly, the
• 16:58
  source notes ulnar nerve injury at the elbow
• 17:00
  is statistically more common with general anesthesia
• 17:02
  than regional. That is interesting. And regional
• 17:05
  risks. Potential risks include nerve injury from
• 17:07
  the needle or catheter, infection, bleeding,
• 17:10
  or hematoma at the site, and rarely local anesthetic
• 17:13
  toxicity if the drug gets into the bloodstream
• 17:16
  accidentally. But, you know, with ultrasound
• 17:18
  guidance now widely used and careful technique,
• 17:21
  these risks are generally quite low. So overall,
• 17:24
  regional seems to be increasingly favored for
• 17:26
  upper limb surgery. For many patients, yes. The
• 17:29
  potential for superior pain control and a smoother
• 17:32
  overall experience makes it a very attractive
• 17:34
  option. This has been incredibly insightful.
• 17:37
  It really drives home the sheer complexity and
• 17:40
  elegance of the hand, wrist, and forearm. and
• 17:43
  the level of precision needed by surgeons supported
• 17:46
  by sophisticated anesthesia. It really is a team
• 17:49
  effort, isn't it? Surgical skill and anesthetic
• 17:52
  management working hand -in -hand for the patient.
• 17:54
  Definitely. And thinking about this intricate
• 17:56
  network we've discussed, it makes you wonder,
• 17:59
  doesn't it, what other seemingly small, compact
• 18:01
  areas of the human body hold similar levels of
• 18:04
  anatomical challenge and fascination for doctors?
• 18:07
  Maybe something for you, our listener, to ponder.
• 18:10
  Thanks for joining us on The Deep Side.