Foot and Ankle - Arthritis and Nerve Entrapment

Welcome to another lecture in the MSK Cornerstone course. This is a continuation of our foot and ankle lecture series. In this lecture, we will address arthritic conditions of the foot and ankle, including tibiotailer and midfoot arthritis, as well as some of the common nerve and tratment conditions encountered in the lower leg and foot. As always, I will try to be comprehensive, including information applicable during clinical practice, but brief enough to touch on key testable material found on common qualification exams. All right, let's get started. We'll start off with some of the common arthritic conditions of the foot and ankle. So first off, imagine a football player that complains of pain over the anterior ankle that is worse when getting in a three-point stance. When in this position, his ankle is in extreme dorsiflexion. The pain has come on gradually over time, but now it has become quite bothersome. In comparison to his contralateral side, he has some swelling, decreased range of motion, particularly with dorsiflexion, and pain that is reproducible with forced dorsiflexion. What diagnosis would you be considering? Tibiotailer impingement. This is typically caused by osteophytes or excessive soft tissue located at the anterior tibiotailer joint and is commonly seen in athletes. A history of overuse or previous injury to the ankle may predispose to developing impingement symptoms. This is present with pain over the anterior ankle that is worse with dorsiflexion. There may be some mild swelling anteriorly and limited dorsiflexion in comparison to the contralateral side. Initial workups should include plain radiographs. Plain radiographs may show osteophyte formation on the anterior distal tibia or dorsal talus. If radiographs are negative, but clinical suspicion remains high for soft tissue impingement, an MRI may be obtained to further evaluate the structures. Anarchists are treated initially with activity modification and anti-inflammatories as needed. High-level athletes and those that fail conservative treatment may undergo an arthroscopic excision of osteophytes and synovectomy to remove any soft tissue impingement. Keep in mind the complications associated with ankle arthroscopy if one of those questions pop up. When removing anterior osteophytes, the dorsal nerve assular bundle, including the deep perineal nerve and anterior tibial artery, are at risk. The anterior lateral portal places the superficial perineal nerve at risk, and the anterior medial portal places the sap and its vein at risk. Alright, our next clinical vignette is a chain-smoking workers' compensation patient that fell off a scaffold at a construction site sustaining a highly-commonuted tibial plafond fracture about seven years ago and has never gotten back to work. You've been following him for a while, but haven't seen him for about a year. Today he comes in stating that he can barely walk. You look at his ankle and sure enough, it looks pretty swollen. Checking his range of motion, you notice it is definitely limited in comparison to the contralateral side. As always, you get some radiographs to see what's going on, but you've already got a pretty good idea given his clinical history. His x-rays come back and his ankle looks awful. Bad tibiotail or arthritis. So ankle arthritis is not incredibly common. When it does occur, it usually falls a previous traumatic injury to the ankle joint. If following a fracture, the ankle joint does not heal in an anatomic position, then the contact forces across the joint will be altered, leading to increased pressure, cartilage loss, and joint space narrowing. Patients with tibiotail or ankle arthritis present with pain on weight-bearing and stiffness at the ankle joint. On exam, they may have swelling or an effusion, or possibly even an obvious joint deformity if there is significant malunion from the previous fracture. These patients will frequently have a decreased range of motion in comparison to the contralateral extremity. All diagnostic studies should include plain radiographs. Radiographs will frequently show common characteristics of osteoarthritis, including joint space narrowing, subchondral sclerosis, and potentially an angular deformity. Now, how do we treat patients with tibiotail or arthritis? Conservative treatment includes an ankle brace or orthotic and anti-inflammatories. A single rocker sole shoe, again, a single rocker sole shoe, may help in that it alleviates the demand for dorsiflexion and plantar flexion at the tibiotail or joint during gait. If conservative treatment fails, there are several surgical options, and the choice of procedure will be dictated based upon patient-specific factors and the degree of pathology. For mild disease with anterior osteophyte formation, arthroscopic resection of bones purse can be performed much like our previously mentioned tibiotail or impingement patient. If the patient has developed asymmetric varus osteoarthritic changes without any significant joint space collapse, a supermallial or osteotomy to correct the overall ankle alignment may be beneficial. For more advanced disease, an arthrodesis or ankle arthroplasty may need to be considered. Arthrodesis or fusion of the tibiotail or joint should be done with the ankle and neutral dorsiflexion between 5 and 10 degrees of external rotation and 5 degrees of hind foot valgus. Adjacent joint degeneration, including the subtailor and talonovicular joint, is common following fusion of the tibiotail or joint. As with any fusion procedure, smokers are at an increased risk for developing a non-union. Total ankle arthroplasty can also be considered, but it is vital to carefully select patients to optimize your success with this procedure. Total ankles are best preserved in low-demand elderly patients with a low BMI. Young active laborers, obese patients, patients with a Charcot ankle or ankle instability are not candidates for a total ankle arthroplasty. In appropriately selected patients, ankle arthroplasty can do very well. As part of the procedure, the syndesmosis must be fused. If the syndesmosis fails to fuse, the total ankle may loosen and require revision or conversion to an arthrodesis. For total ankle arthroplasty, I think the biggest takeaway point is to consider who not to put them in. I'd familiarize yourself with the contraindications and complications of the procedure. Now let's move on to mid-foot arthritis. This is generally an idiopathic condition, however it can also be seen following a trauma such as a Liz Frank injury. Patients complain with pain in the arch of the foot that is worse during the toe-off phase of gait. They may develop a pesplenovalgis deformity with collapse of the arch, forefoot abduction and hind foot valgus. This deformity mimics that of posterior tibial tendon insufficiency that we discussed in our last lecture. Human radiographs will show degenerative changes within the mid-foot and collapse of the arch evident by a depressed miri's angle. Again, what is miri's angle? It is a line between the axis of the talus and the first metatarsal on lateral radiographs. Conservative management of mid-foot arthritis includes anti-inflammatories and a stiff sole shoe or possibly a rocker bottom orthotic shoe. Surgical treatment involves fusion of the arthritic joints in a position that attempts to recreate the normal foot architecture. As with fusion procedures during Liz Frank injuries, generally only the first three rays are fused, leaving the fourth and fifth mobile to help with normal accommodation during gait. If there are significant arthritic changes of the fourth and fifth rays, an interposition arthroplasty can be performed for pain relief. Now let's switch gears and move on to some neurologic issues that surround the foot and ankle that you will commonly encounter in clinical practice and on examinations. We will begin with the very common Morton's neuroma. A Morton's neuroma presents as pain at the area between the metatarsal heads that is worse with weight bearing and shoes that compress the forefoot such as high heels. In fact, these neuromas occur at a 9 to 1 female to male ratio. They are thought to occur due to sustained compression of the interdigital nerves in the area of the transverse intermetatarsal ligament that leads to fibrosis and entrapment of the nerve. Remember that the interdigital nerves are the terminal branches of the medial and lateral plantar nerves that run between the metatarsal heads, plantar, to the intermetatarsal ligament. Patients will complain of four foot pain and possibly peristegias within the web space of the affected nerve. The most commonly affected nerve is the interdigital nerve running between the second and third metatarsal heads. On physical exam, palpation and compression of the neuroma may cause pain or increased peristegias. A Mulder's Click test is performed by palpating the area of the neuroma and squeezing the metatarsal heads together while attempting to feel for a pop or click. Plain radiographs are generally negative in this disorder but useful for ruling out other pathology. An ultrasound can be helpful to confirm your diagnosis. On ultrasound, the neuroma will show up as a hypoechoic mass. A useful tool for confirming your diagnosis is a diagnostic lidocaine injection. A lidocaine injection that not only causes numbness within the nerve distribution but also alleviates the patient's pain can be a useful tool. First-line management for a Morton's Neuroma includes footwear modifications and metatarsal pads. Many patients, however, aren't too happy with trashing a closet filled with expensive shoewear and will opt for alternative treatments. A corticosteroid injection may provide some symptomatic relief, however its efficacy is rather variable. For particularly bothersome cases, the patient can be treated with anorectomy and burying of the proximal nerve stump. This is typically done through a dorsal approach with transection of the intermetatarsal ligament followed by subsequent repair at the end of the case. Patients need to understand that they will be trading pain for numbness. Next up is the great mimicker of plantar fasciitis. The first branch of the lateral plantar nerve, known as Baxter's nerve, can become entrapped on the bottom of the foot and be quite painful. This presents as pain localized over the plantar medial aspect of the foot and commonly occurs in runners. So now in runners, there are three things to worry about with medial heel pain. Stress fractures, plantar fasciitis, and Baxter's nerve entrapment syndrome. One way to differentiate this from plantar fasciitis is the presence of neuritic pain or a positive tenelle sign. This nerve innervates the abductor digity quinty and is compressed by the fascia of the abductor halicus longus and the medial side of the quadratus plantae. This can be treated surgically with release of the abductor halicus fascia. So again, in runners with medial side of heel pain and point tenderness, think calcaneal stress fracture, plantar fasciitis, or Baxter's nerve entrapment syndrome. Let's continue on now with our nerve entrapment talk. You'll notice a common theme when we talk about nerve entrapments, and that is, tunnels seem to cause problems. The carpal tunnel, the cubital tunnel, the tarsal tunnel, which we'll talk about in a second, all seem to cause problems. Sure, they act to house the nerve vascular structures, but in doing so, they can become common sites of compression. Well, which tunnel would be causing the problem in a patient that presents with vague dorsal foot pain and numbness in the first web space? Well, first, what nerve is responsible for sensation in that area? The deep perineal nerve, and what tunnel might be the site of compression? The anterior tarsal tunnel. The medial and lateral borders of the anterior tarsal tunnel are the medial and lateral malleoli. It is bound superficially by the inferior extensor retinaculum of the ankle, and its deep border is the capsule of the tail and ovicular joint. It contains the extensors of the foot and ankle, including medial to lateral, the tibialis anterior, extensor halicus longus, the neurovascular bundle, including the deep perineal nerve and dorsalis pedis artery and vein, as well as the extensor digitorum longus and peroneus tertius. Expression of the deep perineal nerve in the anterior tarsal tunnel most commonly occurs at the inferior margin of the inferior extensor retinaculum. The contents of the tunnel are under increased compression with plantar flexion of the ankle. This also seems to be the exacerbating position as well. As with any nerve compression syndrome, anything that smashes the components of the tunnel is likely to reproduce the symptoms. These can be external or internal causes. The external causes are high heels, tight shoes, or laces. The internal causes include ganglion cysts, tendinitis of one of the extensor tendons or osteophytes, particularly the dorsal osteophytes seen with tibiotail or impingement syndrome. Patients with a pescavus deformity also have an increased risk of developing anterior tarsal tunnel syndrome. Patients will not only present with neurotic symptoms localized in the nerve distribution of the deep perineal nerve, but they also may have some weakness or atrophy of the extensor digitorum brevis. However, this is quite difficult to assess. When else, particularly in the trauma setting, do we think about the extensor digitorum brevis? The EDB is responsible for blocking the reduction during a dislocation. Which dislocation? Remember, medial subtailer dislocations are blocked by lateral structures. Again, so the EDB, or perineal tendons, may block the reduction to a medial subtailer dislocation. Alright, back to anterior tarsal tunnel syndrome. Patients may also have a positive tunnel sign over the deep perineal nerve. Radiographs may show osteophyte formation, but again, many times they are normal. If you are worried about a space-occupying lesion, such as a ganglion cyst or a giant cell tumor of the tendon sheath, an MRI should be ordered to fully evaluate the mass. As with a Morton's neuroma, a diagnostic lidocaine injection can be helpful in confirming your suspicion for anterior tarsal tunnel syndrome. So first-line treatment is focused on removing compression at the tunnel. As plantar flexion increases pressure of the tunnel and can exacerbate the conditions, it may be time to tell the patient to ditch the high heels. Again, there may not be a ton of patient compliance with this treatment. A local corticosteroid injection may provide some relief. If the patient fails all conservative treatment, a surgical release of the inferior extensor retinaculum may be performed with excision of any dorsal osteophytes. Well now we've talked about anterior tarsal tunnel syndrome, which by our amazing deductive reasoning skills implies the existence of a posterior tarsal tunnel syndrome. However, posterior tarsal tunnel syndrome is so much more common and so much more famous that it actually just goes by tarsal tunnel syndrome. So what makes up the posterior tarsal tunnel? Superficially, the structures are bound by the flexor retinaculum, which is a tough fibrous band that runs from the medial malleolus to the medial aspect of the calcaneus. The deep border of the tunnel is the calcaneus and talus. The contents of the posterior tarsal tunnel, including from anterior to posterior, the tibialis posterior, the flexor digitorum longus, the posterior tibial artery and nerve and the flexor halicus longus. As the nerve travels through the tunnel, it divides into three branches. The calcaneal branch and the medial and lateral plantar branches. Causes of compression within the tunnel are similar to those of anterior tarsal tunnel syndrome. Extrinsic causes include compression from shoe wear, previous trauma leading to bony malignment, scarring, or lower extremity edema. Intrinsic causes include swelling of the tendon sheets from tinosinivitis or tendinopathy, ganglion cysts, or underlying osteophytes. Posterior tarsal tunnel syndrome can occur concurrently with posterior tibial tendon insufficiency as a result of both pesplanus deformity causing compression of the tunnel and any tendinopathy associated with the posterior tibialis tendon. Patients with tarsal tunnel syndrome will typically present with pain over the plantar or medial aspect of the foot that is worse with prolonged standing and activity. They may also complain of peristhesia in the plantar nerve distribution which can help to differentiate this from plantar fasciitis along with a lack of medial sided point tenderness. On exam, they may have a tenelle sign over the tibial nerve. Bore deflection in EE version or sustained manual compression of the tarsal tunnel will exacerbate the symptoms. With long standing compression, the foot intrinsic musculature may show somatrophy. Plain radiographs should be evaluated for any obvious bony abnormality causing compression, however any soft tissue pathology will need to be assessed with an MRI. An EMG can be helpful to confirm your diagnosis. Sensory latency are typically more frequently prolonged than motor, however there may be decreased motor action potentials to the abductor hallicus or abductor digitiminimii. Alright, so again, how do we treat these patients? Conservative management of tarsal tunnel syndrome includes bracing or anti-inflammatories, however there does not seem to be a very high success rate with these treatments. Patients that are indicated for surgery have a similar diagnostic workup as those with carpal tunnel syndrome. They have a history and physical exam consistent with the diagnosis, a confirmatory EMG analysis, for a reason for compression on imaging and have failed three months of conservative treatment. If they meet all of these criteria then a surgical decompression by release of the superficial constricting structures is indicated. As mentioned in our anatomic review, this includes more than just the flexor retinaculum. The deep fascia of the leg that blends with the proximal margin of the retinaculum as well as the distal abductor hallicus fascia should also be in size to ensure an adequate decompression of the nerve has been performed. Recurrence in this condition is most commonly due to inadequate release of the overlying structures. Alright, that concludes our discussion on arthritis of the foot and ankle as well as some of the common neurologic entrapment syndromes that we see around the foot. The next lecture will focus specifically on the manifestation of diabetes in the foot and ankle including diabetic foot ulcers and the development of a Charcot foot. As always, please check back frequently for lecture updates and modifications. Thanks for listening.