The lumbosacral plexus starts from L4 to S4. The lumbar
plexus starts from L1 to L4. It has 6 branches. To remember this, think “I
Twice Got Lunch on Friday”. Knee extension is done by muscles that are
innervated by the L2, L3, and L4 nerve roots via the femoral nerve. The femoral
nerve innervates the muscles of the anterior compartment of the thigh
(quadriceps). th
lumbar nerve root. All nerves except the genitofemoral nerve and the obturator
nerve emerge from the lateral aspect of the psoas major muscle. The
genitofemoral nerve emerges anteriorly, and the obturator nerve emerges
medially in relationship to the psoas major muscle. L2, L3, and L4 will give
the obturator and femoral nerves. The obturator nerve and the femoral nerve are
equal.
The femoral nerve also provides sensation to this area. These
muscles cause hip adduction: adductor brevis, adductor longus, and adductor
magnus. They are innervated by the L2, L3, and L4 nerve roots via the obturator
nerve. This is the area of sensation supplied by the obturator nerve. With its
origin coming from the nerve roots of L2 and L3, the lateral femoral cutaneous
nerve of the thigh innervates the skin on the lateral part of the thigh. Risk
of injury to this nerve can occur with bone graft, with hip or acetabular
procedures, and with external fixator of the pelvis. The genitofemoral nerve
comes from the L1 and L2 nerve roots. Six branches come from the lumbar plexus.
Two branches come from one nerve root. Two branches come from three nerve
roots. Two branches come from two nerve roots. The two nerves that arise from
one nerve root are: iliohypogastric and iliolinguinal. Both of these nerves arise
from L1 nerve root. The iliohypogastric nerve is above the iliolinguinal nerve.
The two nerves that arise from two nerve roots are the genitofemoral (L1, L2)
and the lateral femoral cutaneous nerve of the thigh (L2, L3). The two nerves
that arise from three nerve roots are the obturator and the femoral. Both arise
from the L2, L3, and L4 nerve roots. There is also contribution from T12. The
fourth lumbar nerve root also passes a branch to the lumbosacral trunk at the 5
The ulnar nerve arises from the medial cord of the brachial
plexus. After the ulnar nerve passes through the arm, it runs from the medial
epicondyle to the pisiform bone in the wrist in a direct trajectory. Two carpal
bones are important in relation to the ulnar nerve in the wrist: the pisiform
and the hamate. Both the ulnar nerve and the ulnar artery enter the Guyon’s
canal. The Guyon’s canal is approximately 4 cm long. The ulnar nerve enters the
wrist medial to the ulnar artery. The Guyon’s canal has one proximal entrance
and two distal exits, one superficial and one deep. The Guyon’s canal contains
the ulnar nerve with its superficial sensory and deep motor branches. th
lumbricals. The deep branch of the ulnar nerve also innervates the hypothenar
muscles, the adductor pollicis muscle, and the deep head of the flexor pollicis
brevis muscle. The superficial branch of the ulnar nerve is mainly sensory. It
gives supply to the digital nerves of the 4th and 5th
fingers and a motor branch to the palmaris brevis muscle. Based on the location
of compression in the Guyon’s canal, the affected area of the nerve may be
purely motor, purely sensory, or a mixture of motor and sensory. Pain and
paresthesia in the ulnar 1 ½ digits or clawing of the 4th and 5th
fingers can be symptoms. Another symptom can be loss of function of the
intrinsics (it normally flexes the MCP and extends the IP joints). In low ulnar
nerve injury, the flexor digitorum profundus is working (functional). It flexes
the 4th and 5th fingers and causes clawing (unopposed by
the intrinsic muscles). Ulnar nerve palsy results in paralysis of the intrinsic
muscles; test the first dorsal interosseous muscle and check for atrophy. 70%
of pinch is lost due to loss of adductor muscles.th and 5th
fingers and causing clawing of these two fingers. High ulnar nerve palsy has
less clawing of the 4th and 5th fingers and sensory
deficit to dorsum of the hand. In cubital tunnel syndrome (high ulnar nerve
involvement) you can also find Tinel’s sign at the elbow and positive elbow
flexion test. The dorsal cutaneous branch arises before the Guyon’s canal. If
you have high ulnar nerve palsy, there will be sensory deficit on the dorsum of
the hand, because that nerve will be affected. If you have a low ulnar nerve
palsy, that nerve will not be affected because it already branched out or came
off from the ulnar nerve and escaped (sensation on that part of the dorsum of
the hand). Nonoperative treatments include activity modification, NSAIDS, and
splinting. Surgical treatment includes release of the carpal tunnel .In
patients diagnosed with both carpal tunnel and ulnar tunnel syndrome, the
Guyon’s canal is adequately decompressed by the release of the carpal tunnel. Local
decompression can be done especially if nonoperative treatment fails.
Decompression of the ulnar nerve by addressing the cause; success of surgery
depends on finding a cause. To determine the cause of compression, explore and
release of all three zones in the Guyon’s canal, vascular treatment of ulnar
artery thrombosis, hook of hamate excision, decompress ganglion cysts, and
release hypothenar muscle origin. All of these things are possible causes that
need to be addressed. Tendon transfer can be a treatment in late cases; it will
correct claw fingers, restore power pinch, and improve Wartenberg’s sign.
The Froment’s test is
positive. When pinching a piece of paper between the thumb and index finger,
the thumb IP joint will flex if the adductor pollicis muscle is weak due to
ulnar nerve palsy. Symptoms also include weak grasp due to intrinsic weakness,
Wartenberg’s Sign, and the Allen’s test. Carpal tunnel view x-rays and CT scans
are useful to evaluate hook of the hamate fractures and nonunions. MRI is
useful to evaluate ganglion cysts. Ultrasound is useful to check vascular
status of the hand and to diagnose ulnar artery thrombosis. EMG and nerve
studies are helpful. High or low ulnar nerve injury is a differential
diagnosis. In low ulnar nerve injury or compression, the flexor digitorum
profundus muscle is working; flexing the 4
The
Guyon’s canal contains the ulnar nerve with its superficial sensory and deep
motor branches. Ulnar nerve compression neuropathy can occur in the Guyon’s
canal. The most common causes include volar ganglion, hook of hamate fracture,
repetitive trauma, ulnar artery thrombosis, palmaris brevis muscle hypertrophy,
or pisiform fracture or dislocation. Volar ganglion cysts may protrude or grow
into the canal, which could compress the ulnar nerve. Hook of hamate fracture
can lead to neuropathy of the nerve in the tunnel. Compression and inflammation
also can result from repetitive trauma such as using a hammer. Trauma over the
hook of hamate, where the superficial branch of the palmar artery lies, leads
to vascular insufficiency of the ulnar side of the hand. Ulnar nerve
compression may occur as a result of pisiform dislocation or fracture. The
Guyon’s canal is bound on the floor by the transverse carpal ligament, on the
roof by the volar carpal ligament, on the ulnar border by the pisiform and
pisohamate ligament, and on the radial border by the hook of hamate. There are
three zones of Guyon’s canal compression. Zone I is located proximal
bifurcation of the nerve; it is characterized by mixed motor and sensory
symptoms, and it is caused by ganglia and hook of hamate fractures. Zone II is
located in the deep motor branch; it is characterized by motor symptoms only,
and it is caused by ganglia and hook of hamate fractures. Zone III is located
by superficial sensory branch; it is characterized by sensory symptoms only,
and it is caused by ulnar artery thrombosis or aneurysm. The deep branch of the
ulnar nerve innervates all of the interosseous muscles and the 34d and 4
The reverse pivot shift test helps to diagnose acute or
chronic posterolateral instability of the knee. A significantly positive
reverse pivot shift test suggests that the PCL, the LCL, the arcuate complex,
and the popliteal fibular ligament are all torn. The reverse pivot shift test
begins with the patient supine with the knee in 900 flexion. Valgus
stress is then applied to the knee with an external rotation force. Bring the
knee from 90o of flexion to full extension. The tibia reduces from a
posterior subluxed position at about 20o of flexion. A shift and
reduction of the lateral tibial plateau can be felt as it moves anteriorly from
a posteriorly subluxed position. This is called the reverse pivot shift because
shift of the lateral tibial plateau occurs in the opposite direction of the
true pivot shift (seen in ACL tears). If the tibia is posterolaterally
subluxed, the iliotibial band will reduce the knee as the IT band transitions
from a flexor to extensor of the knee. It is very important to compare this
test to the contralateral knee. The pivot shift test indicates an ACL tear. The
reverse pivot shift test indicates posterolateral instability of the knee.
Posterolateral corner injury includes the LCL, popliteal fibular ligament,
arcuate complex, and the lateral capsule.
The anterior cruciate ligament is located in the front of
the knee. Rupture of the anterior cruciate ligament (ACL) is a condition
commonly seen in sports usually due to a non-contact pivoting injury. The Pivot
Shift test is a specific test for ACL deficient knee (ACL injury). Pivot shift
is pathognomonic for an ACL tear and is best demonstrated in a chronic setting.
Lachman’s test is the most sensitive examination test for ACL injury. o of flexion. The anteromedial bundle is
tight in flexion, and it increases anterior translation at 90o of
flexion. The Lachman’s test is the most sensitive test especially in acute
settings, and the examiner will find no end point with anterior translation of
the tibia. In an acute setting, physical examination can be difficult or
limited due to pain. With the Pivot shift test, the patient must be completely
relaxed, and the test is helpful in chronic situations especially if the
patient complains of the knee giving way.
In the Pivot shift, the knee subluxes
in extension and reduces at 20-30 degrees of flexion. The Pivot shift
correlates closely with patient satisfaction of their reconstructed knee. It is
a measure of functional instability following ACL reconstruction. Vertical
femoral tunnel placement will cause rotational instability seen as a positive
pivot shift, and the malposition of the bone tunnel will be seen in an AP view
x-ray of the knee. The 9 or 10 o’clock position is better than the 12 o’clock
position; the vertical position is bad. The patient with an ACL injury usually
has a non-contact pivoting injury event with an awkward landing, feeling a
“pop” sensation, or immediate swelling. Aspiration usually shows blood in the
knee which proves a 75% chance of ACL tear when you aspirate blood from the
knee. Patients will also exhibit a positive Lachman’s test which may be hard to
examine because of the pain. Aspiration of the knee may make the examination
easier. MRI of the knee joint will show the hematoma, and it may show bone
lesions or bruising in the typical location which is characteristic with tears
of the ACL. These injuries are typically located at the middle of the femoral
condyle and posterior part of the tibia laterally. You may find a triple injury
within the MRI (O’Donoghue’s Unhappy Triad). The O’Donoghue’s Unhappy Triad
include an anterior cruciate ligament (ACL) injury, a medial cruciate ligament
(MCL) injury, and a lateral meniscus injury. In chronic ACL tears, the posterior
horn of the medial meniscus is the most commonly injured structure. In acute
ACL tear, send the patient for therapy for range of motion, brace the patient
and allow the MCL to heal and reconstruct the ACL later if needed. Patients
should do stress hamstring therapy in ACL tears. The patient will probably
complain of instability immediately or later on.The tibia can be pulled forward more than
normal (anterior translation). The examiner will have a sense of increased
movement and lack of a solid end point. For the pivot shift test, the patient
should be lying supine and totally relaxed. With pivot shift, the knee is in
the subluxed position when the knee is in full extension. The pivot shift
starts with extension of the knee and you can feel a “clunk” at 20-30 degrees
of flexion. To perform, hold the knee in full extension then add valgus force
plus internal rotation of the tibia to increase the rotational instability of
the knee. Then take the knee into flexion. A palpable clunk is very specific of
an ACL tear. The iliotibial band will reduce the tibia and create the clunk on
the outside of the knee. Always compare with the other side. The ACL prevents
anterior translation of the tibia. It is a secondary restraint to tibial
rotation and varus and valgus stress. The ACL consists of two bundles: the posterolateral
bundle and the anteromedial bundle. The posterolateral bundle prevents pivot
shift, contributes to rotational stability, prevents internal rotation of the
tibia with the knee in near extension, and increases the anterior translation
and tibial rotation at 30
The ACL
keeps the tibia from sliding out in front of the femur and provides rotational
stability to the knee. Rupture of the ACL causes anterolateral rotatory
instability. The tibia moves anterolaterally in extension; however, when you
flex the knee, the IT band becomes a flexor of the knee. The IT band pulls back
and reduces the tibia. The pivot shift test goes from extension (tibia
subluxed) to flexion, with the tibia reduced by the iliotibial band. Both the
Lachman’s tests and the Pivot shift test are associated with 20-30 degrees of
knee flexion. The Lachman’s test starts at 20-30 degrees of flexion. With the
Pivot shift test, you feel the clunk at 20-30 degrees of flexion. 20-30 degrees
of flexion is important for examination of the ACL. For the Lachman’s test, the
femur is stabilized with one hand and the other hand pulls the tibia anteriorly
and posteriorly against the femur.
