As with any peripheral nerve surgery, tarsal tunnel surgery is demanding and can sometimes be excessively difficult. Additionally, one may not have a full appreciation of the outcome until some point in the postoperative period — if at all — when the nerve has had adequate time for recovery and/or regeneration.
Sadly, there are many misnomers in podiatric medicine and surgery. For example, the nomenclature of “tarsal tunnel syndrome” implies that the site of chronic nerve entrapment is at the level of the tarsal tunnel, which actually resides beneath the laciniate ligament or flexor retinaculum at the level of the medial ankle. In reality, this is rarely a source of entrapment.
It would be more accurate to clarify this condition as “multiple nerve entrapment at the medial ankle” as this condition almost always involves entrapment of the medial and lateral plantar nerves, and frequently involves the medial calcaneal nerve as well. Anatomically, the tarsal tunnel is the area proximal to the superior edge of the conjoined edges of the deep and superficial fascia of the abductor hallucis muscle. This is where the medial and lateral plantar nerve tunnels begin. It is analogous to the human forearm wrist fascia in the upper extremity. It is well known in carpal tunnel surgery that the median nerve is rarely entrapped at this level but actually occurs distally beneath the volar carpal ligament.
There are many small factors that contribute to and differentiate successful “tarsal tunnel surgery” versus those surgical interventions that may not be ultimately successful or, in some cases, are detrimental for the patient. Most of these factors can be boiled down into three areas: preoperative considerations and diagnosis; intraoperative surgical technique; and postoperative management.
A Guide To Essential Preoperative Considerations
Diagnosing this condition can sometimes be difficult and confusing for the physician. Patients occasionally have nebulous descriptions, which many times do not fit with the clinician’s clinical perspective or ideation. It is not unusual for the patient to complain of a wide array of symptoms during their history of present illness.
Tarsal tunnel syndrome is frequently associated with other lower extremity pathology such as recurrent Morton’s neuroma. It may be masked by other pathology such as heel pain that is attributed only to plantar fasciosis.1
Heel pain is the most common reason a patient seeks podiatric care and the percentage of patients with nerve entrapment can be very high. Rose, et al., showed that nerve entrapment occurred in 72 percent of 97 patients who presented with heel pain.2 We have seen the same presentation with involvement of the medial calcaneal nerve, with or without additional entrapment of the nerves in the medial ankle.
When one obtains a history of present illness, there are key statements that should raise some flags for physicians. These statements include: “It gets worse throughout the day,” “it hurts at night — even when I am not on it,” “the orthotic makes it worse” and “there is a full feeling in my ankle.” It is also not unusual for patients to say they have heel pain but the pain has a different nature than when they were first treated for their plantar fasciosis. Any of these telling statements by the patient should clue the practitioner into expanding the investigation not only to ascertain nerve entrapment but also to identify potential systemic disease, which could be the etiology of the patient’s condition.
It is important to obtain a complete history from patients when they present with a clinical complaint that may include nerve entrapment of the medial ankle. A history of prior inversion ankle sprain(s) or injury can be an important factor to consider even if the event occurred long before the presentation of symptoms. Any family history of diabetes is important as is the morphology of the patient. If the patient has not been diagnosed with diabetes and he or she is obese, one strongly needs to consider a referral for medical consultation and laboratory studies.
Indeed, it is imperative that physicians understand that entrapment of one or more of the medial ankle nerves is rarely an isolated condition but more generally a symptom of something more complex. Patients with multiple etiology heel pain syndrome (MEHPS) frequently present to the tertiary clinical center after months or years of failed treatment. In other cases, one may see patients, who had previously been diagnosed with plantar fasciosis, present because they only had partially successful treatment. Further clinical examination and diagnostic testing often turns up an etiological factor of nerve entrapment.
Pertinent Keys To Diagnosing Tarsal Tunnel Syndrome
In regard to the clinical examination and testing, physicians should perform provocation testing and determine the presence or absence of a Tinel’s sign. It is possible for any clinician to elicit a parasthesia with very heavy percussion to a nerve, even in areas of no entrapment, if delivered by a neurological hammer. This should not be considered diagnostic or a positive Tinel’s test. When slight pressure over the course of the tibial and medial plantar nerve elicits discomfort from the patient, especially in comparison to the contralateral side, these should be strong indicators of nerve entrapment at those levels.
It is important to reiterate that surgical intervention can only be successful for the patient if the surgeon makes a complete, thorough and accurate preoperative diagnosis.
When it comes to electrodiagnostic studies, one may receive a negative or inconclusive neurological report even in the face of overwhelming clinical findings and the history of present illness. The incidence of false negatives with traditional electrodiagnostic studies in patients with tarsal tunnel syndrome can be greater than 50 percent.
Even when one has clinically established the diagnosis as tarsal tunnel syndrome, there are varying degrees of nerve entrapment and subsequent axonal degeneration. Currently, the only accurate way to determine the level of axonal degeneration is via neurosensory testing with the PSSD (Pressure Specified Sensory Device, Sensory Management Systems).3
Understanding The Impact Of Patient Education On Surgery Expectations
Preoperative educational counseling is imperative to success with lower extremity peripheral nerve surgery. When the surgeon does not offer a full explanation of realistic postoperative expectations, the outcomes can be less than desired by both surgeon and patient due only to subjective aspects. This applies regardless of the quality technique or experience a surgeon brings to the table.
Peripheral nerve regenerates variably and, in severe longstanding cases, relatively little. One can assure the patient that the longer the nerve has been entrapped, the less chance there will be for complete neural regeneration. Brown, et al., documented this well in the upper extremity with an analysis of more than 12,000 cases of carpal tunnel decompression.4
However, one should determine if the patient has had prior carpal tunnel surgery. Chris Maloney, MD, a Professor at the University of Arizona, has demonstrated that patients who have had previously successful carpal tunnel decompression surgery have a high likelihood of improvement from surgery in the lower extremity with peripheral nerve decompression.5-7
If there has been any type of intervention in the area of the tibial nerve (such as steroid injections, treatments with cryotherapy or sclerosing injections), the surgeon must be wary of peripheral nerve injury in addition to entrapment. One also needs to counsel the patient about this as any of these types of treatments can cause permanent peripheral nerve injury, which would decrease the likelihood that a neurolysis/decompression would improve the patient’s condition.
Six Essential Facets To Facilitating Surgical Success
Neuroanatomy is probably the most variable of all human tissues. Often, surgeons see a different anatomical presentation than what they anticipated preoperatively. Lower extremity peripheral nerve surgery is demanding and exact.
The overall success of this procedure is dependent upon one addressing many little concerns — which by themselves would probably not affect the overall outcome in osseous or other types of surgery — in the most judicious and appropriate manner possible to ensure an optimal outcome.
However, there are some general principles that will strongly contribute to the best possible outcome for those who undergo tarsal tunnel decompression surgery. These principles include:
• proper incision placement;
• loupe magnification;
• tissue handling;
• internal neurolysis only when indicated;
• use of bipolar cautery for meticulous hemostasis; and
• skin closure.
Emphasizing Proper Incision Placement And Tissue Handling
Proper incision placement. Accurate skin incision placement is critical in tarsal tunnel decompression surgery because the surgeon must access four distinct nerves and anatomical sites. The surgeon must achieve proper neurolysis for all of the following nerves: tibial nerve, medial plantar nerve, lateral plantar nerve and medial calcaneal nerve(s).
Postoperative wound dehiscence is one of the most frequently cited complications of this surgery as the proper incision placement requires a nearly perpendicular orientation to the relaxed skin tension lines in the medial ankle area.
To gain adequate access to all of the nerves one needs to decompress, the surgeon needs to orient the incision in such a way that at the distal extent, it does not deviate too far anterior over the medial plantar nerve tunnel or posterior over the lateral plantar nerve tunnel. In regard to the incision, one should ensure equidistant placement between the topographical estimation of the locations of the medial and lateral nerve tunnels. This allows adequate exposure to identify and address the medial calcaneal nerve(s), and simultaneously provides good exposure to the medial plantar nerve.8,9
There are cases in which one places the incision too far anterior over the medial plantar nerve. Accordingly, the surgeon is unable to address lateral plantar nerve entrapment and the patient has continued pain and symptoms.
Tissue handling. One must emphasize delicate soft tissue handling and be particularly gentle in the handling of the peripheral nerve. Simple things like avoiding the use of sharp Senn retractors can improve overall outcomes of peripheral nerve surgery. Ideally, the surgeon should never grab the nerve with forceps but rather push the neural tissue with the side of the forceps. Never place the nerve between the teeth of the forceps as one may not be aware of how much pressure he or she is exerting with the instrument.
In cases of internal neurolysis, in which one must grasp the neural tissue, be sure to use microsurgical forceps and only grasp the epineurium. Surgeons cannot achieve this without loupe magnification. Any fascicle that one grasps will be damaged and potentially become symptomatic.
Why Loupe Magnification Plays A Vital Role
Loupe magnification. It is impossible to facilitate intraoperative assessment of peripheral nerve and optimal outcomes without the use of loupe magnification. Use at least 3x power. Good surgical loupes are expensive and should be fitted for the surgeon by a custom vendor.
It is my opinion that one cannot overspend on getting the proper fit and best optics when purchasing surgical microscopes. This is not only a serious economic investment but one that is required to help ensure the desired patient outcome.
What You Should Know About Internal Neurolysis And Hemostasis
Internal neurolysis. Fortunately, most tarsal tunnel decompressions do not need internal neurolysis. However, one can only make the intraoperative decision of whether it is necessary to perform internal neurolysis with proper loupe magnification, inspection and microsurgical experience. When the peripheral nerve surgeon begins an internal neurolysis, the surgery has progressed into another level of difficulty and potential danger for the patient. Only those surgeons who have had formal microsurgical training and have the proper surgical loupes and microsurgical instrumentation should perform this aspect of the surgery. This is an area where the patient can simply become worse because of the inherent risks of working inside the nerve.
Hemostasis. All people develop postoperative fibrosis as it is a natural physiological response to trauma or surgery. Some patients are more prone to hypertrophic development than others. Patients who have keloid or hypertrophic scars should raise warning flags in the minds of the surgeons who are planning their surgery. It is well known that meticulous hemostasis decreases postoperative scarring and improves surgical outcome. For all small bleeders one encounters during the case (and surgeons can only visualize these with surgical loupe magnification), he or she must cauterize them with bipolar cautery. The use of monopolar cautery (bovie) in peripheral nerve surgery is dangerous, and can cause irreparable nerve damage from uncontrolled thermal destruction. Surgeons do not need to ground the patient with bipolar cautery.
How To Facilitate Smoother Skin Closure
Skin closure. The most common complication of tarsal tunnel decompression is probably postoperative wound dehiscence. Experience has led to the development of closure techniques that have minimized this complication. Since the incision required to adequately expose the neuroanatomy in this area is nearly perpendicular to the relaxed skin tension lines and is in a flexural area, it is more susceptible to slower and more difficult healing.
We have found that by using 4-0 Monocril sutures on a P-3 needle, placing them intradermally with the buried knots and subsequently using stainless steel surgical staples, wound dehiscence is now almost completely avoidable. I would also recommend leaving the staples in for up to four weeks, if necessary, in certain patients. While staples evert the skin nicely and are less likely to cause ischemia to the wound like a running suture would, they also seem to provide a biofeedback mechanism to the patient. We encourage patients to move their foot and ankle postoperatively, but the staples seem to remind them when they are ambulating excessively.
Key Pearls For Postoperative Management
All podiatric surgeons know that the greatest intraoperative surgical work can be undone in a matter of little time with improper postoperative management.
We recommend placing a small amount of dexamethasone phosphate into the surgical areas after closure to decrease fibrosis around the nerve. Long acting local anesthetics are also useful for pain management, which can have an effect on post-op range of motion. Using a modified Robert Jones dressing has proven to be very useful as it allows some movement for patients but still protects them. A removable walker boot is not recommended as this may place too much pressure on the patient’s wounds.
It is recommended that patients begin active, gentle range of motion exercises the day of surgery, and continue them for a minimum of eight weeks. Educate patients that “nerves need to slide and glide just like tendons.” Sadly, I have had numerous revision cases referred to us because a physician placed the patient into a below knee cast immediately after the surgery and the patient simply scarred back down. Some of these patients were more symptomatic after their surgery than before.
The use of pregabalin (Lyrica, Pfizer) has been beneficial. I recommend all our nerve surgery patients begin the medication prior to surgery, if they are not already on it, and continue to have them take the medication for months postoperatively.
Since patients who have chronic severe pain with peripheral nerve entrapment often have psychological issues as a result, I would recommend preoperative consultation with a psychiatrist who has an emphasis in biological psychiatry. It only makes sense that the peripheral nerve one is treating is connected to a central one that is trying to down-regulate the stimulus generated peripherally. The attention to the patient’s central nervous system can mitigate many postoperative issues and only contribute to the success in managing the whole patient.
Tarsal tunnel decompression surgery is demanding and encompasses many pre- and post-op considerations. If one can address all variables, the success of tarsal tunnel neurolysis can be extremely predictable and high, provided the surgeon has proper training, exacting technique and a strong attention to detail.
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