Most peroneal tendon ruptures are the result of an inversion ankle sprain.
During an ankle sprain the peroneal tendons pull up against the outside of the
ankle to restrain the rolling motion of the ankle. The force applied to
the peroneal tendons can be enough to contribute to a tear (rupture) of the
tendon. Most tears of the peroneal tendons are partial ruptures called
longitudinal tears. One would
tend to think of a tendon rupture as an appositional tear of the tendon, like a
complete tear in a rope or piece of string. But most tears of the peroneal
tendons occur along the course of the peroneus brevis tendon an look much like a
partial or complete split in the peroneus brevis tendon.
During an ankle sprain, as the ankle begins to roll, the
peroneal tendons fire to stabilize the ankle and prevent the sprain from occurring. Both
tendons are pulling up against the downward force of the lateral ankle. The
fibula (lateral ankle bone) becomes a wedge carrying body weight down toward the
ground. As the fibula drives downward, the peroneal tendons pull up against the
ankle and are compressed. The peroneus brevis tendon is adjacent to the fibula
while the peroneus longus tendon runs to the outside of the brevis. A longitudinal tear occurs when the
peroneus longus tendon actually pulls so hard that it
transects (slices) the brevis tendon into two parts along its' length. This means that the
injury is actually caused by one peroneal tendon (the longus) transecting the other
peroneal tendon (the brevis).
The peroneus longus tendon is not immune from injury. Partial and complete ruptures of the peroneus longus tendon do occur but are
far less common than injuries seen in the peroneus brevis tendon. The weakest
portion of the peroneus longus tendon is the point
where it changes direction and rounds the plantar surface of the cuboid. When ruptures of the
peroneus longus do occur, they tend to be found just distal to the plantar
cuboid and are also longitudinal. Complete transverse ruptures of the
peroneus longus tendon are rare.
Another uncommon injury of the peroneus longus tendon is the rupture of the
tendon at the site of an os peroneum. The os peroneum is a small accessory bone found within
the peroneus longus tendon at the lateral wall
of the cuboid. The occurrence of an os peroneum in the general population
is reported in the literature to be 5-26%. When present, a healthy, functioning os peroneum
will help facilitate the transfer of load carried by the peroneus longus as it
rounds the cuboid. Bipartite (two part) os peroneum are common.
Bipartite os peroneum and fractured os peroneum can be difficult to
differentiate. When viewed on x-ray, a bipartite os peroneum will
typically have smooth edges while a fractured os peroneum will display ragged
edges.
Treatment Of Peroneal Tendon Ruptures
Initial care of peroneal tendon ruptures includes much of the same care
recommended for ankle sprains; rest, ice,
elevation, compression and anti-inflammatory medications.
A 4-6 week period of conservative care is warranted before obtaining further
testing such as an MRI. Use of a walking cast
or ankle
brace
may help to splint the peroneal tendons during conservative care. Most peroneal
brevis tendon ruptures do not heal and will require surgical repair.
Following
a lateral ankle sprain, if the lateral ankle is still painful at 6 weeks post
injury an MRI may help to determine whether the peroneal tendons have sustained
an injury. Alternatively, diagnostic ultrasound may be used to evaluate
partial ruptures of the peroneal tendons. MRI is not always 100% accurate when
evaluating peroneal tendon pathology. Many cases of peroneal tears are too
small to find with an MRI or ultrasound and can only be found with direct
visualization during surgery. Occasionally, an accessory tendon known as
the peroneus tertius is present within the peroneal tendon sheath and is
misdiagnosed on MRI as a tendon tear.
The following images show the steps used to perform a repair of a severe
longitudinal tear of the peroneus brevis tendon. Image 1 shows
pre-operative planning outlining the leg and fibula to the left along with the
5th metatarsal and toes to the right. Image 2 shows dissection through the
subcutaneous space and entry into the combined sheath of the peroneal tendons.
Image 3 shows the initial appearance of the damaged peroneus brevis tendon.
Image 4 shows the dissection of the injury in greater detail. The peroneus
brevis tendon shows myxoid degeneration (scaring) and multiple tears.
Image 5 shows an intact peroneus longus tendon with mildly reactive synovium
lining the inside wall of the peroneal tendon sheath. This reaction is due
to chronic inflammation within the tendon sheath. Image 6 show the
repaired peroneus brevis tendon. Also very clear in this image is the
peroneal retinaculum. And image 7 shows final skin closure.
Surgical repair of a longitudinal peroneus brevis tear can be performed on an outpatient basis using
sedation and local anesthesia or general anesthesia. The procedure takes about
approximately 45 minutes to complete. Following repair, most doctors will
limit ambulation to partial weight bearing for a period of days to weeks. No
casting is necessary as early non-weight bearing range of motion is desired.
Return to normal activates depends upon the severity of the tear and success of
the surgery. Most patients are back to 75% of normal activities by 4 weeks
post surgery.
In severe cases of peroneus brevis or peroneus longus tears, including
complete ruptures, treatment options do vary. Tenodesis (fixation of the
tendon) of the damaged tendon may be completed by permanently attaching the
tendon to the cuboid, calcaneus or adjacent tendon. For instance, in cases
of severe peroneus brevis ruptures, the peroneus brevis tendon may be
permanently attached (tenodesed) to the peroneus longus tendon. Other
options include the use of a graft jacket or tendon graft.
In cases of a symptomatic os peroneum or fractured os peroneum, the majority
of cases can be resolved with simple excision of the os peroneum. Excision
of the os peroneum can be performed with a general anesthetic or a local
anesthetic with sedation. Recovery varies and depends upon the integrity
of the peroneus longus tendon follow the surgery. The peroneus tendon will
be weakened by excision of the os peroneum but will regain full strength over
several months. Limitations on ambulation post surgery depend upon the
surgeons impression of the status of the tendon post-op. Limitations may
include non-weight bearing or partial weight bearing for a period of 6-8 weeks
post op.
