How To Address Key Biomechanical Issues With Second MPJ Injuries
Q: A common dilemma is differentiating a neuroma in the second interspace from pathology in the second MPJ. In terms of conservative treatment, is it important to nail down the exact pathology? How do you do this?
A: One will commonly see localized edema within plantar plate injuries of the second MPJ. This may also cause irritation to the plantar digital nerves that are adjacent to the plantar plate area, according to Dr. Kirby. He says careful manual examination of the plantar MPJ area will reveal that the majority of plantar plate injuries are the most tender just proximal to the central aspect of the proximal phalanx base. Dr. Kirby adds that plantar digital nerve irritation, or neuritis, will be most tender either medially or laterally, off-center, from the second MPJ.
Furthermore, Dr. Kirby says plantar plate injuries will often be painful with plantarflexion testing of the digit at the MPJ and this finding is uncommon with neuromas. In addition, a neuroma by itself will not likely be associated with plantar MPJ edema, which Dr. Kirby says is the case in plantar plate injuries.
“Therefore, if you see a swollen second MPJ with classic plantar plate tenderness that also has burning and numbness in the second intermetatarsal space, think secondary interdigital neuritis caused by plantar plate injury, not neuroma,” advises Dr. Kirby. Dr. Bouché confirms plantar plate pathology with clinical use of the Lachman (dorsal drawer or vertical stress) test. He says one can confirm a plantar plate tear with an arthrogram using X-ray or MRI.
Dr. Bouché says there may be plantar plate attenuation if one administers a local anesthetic injection and the amount of local anesthetic injected exceeds 2 cc. He notes that the usual capacity for a local injection in the second MPJ is 1 to 1.5 cc.
Whether one is dealing with pathology in the second MPJ or an interspace neuroma, Dr. Clough says the basic problem is that the second and third MPJs, and the intrametatarsal space are being overloaded. Inevitably, the nerve in the second interspace is often involved to some degree in the inflammatory process, according to Dr. Clough. In most situations, he says it is not critical to differentiate between a neuroma and pathology at the joint level.
“In either situation, your basic task is trying to offload that portion of the foot and re-establish proper mechanics of the first MPJ in order to get the first ray to plantarflex into the ground and accept more weightbearing,” notes Dr. Clough.
Dr. Clough has seldom seen a large neuroma in the second intermetatarsal space. If this condition is present, he notes one will see diminished sensation in the distribution of the digital proper nerve branches in the second and third digits. In these cases, Dr. Clough says simple offloading of the second and third MPJs will fail. He believes such a diagnosis is mainly one of exclusion when symptoms persist despite objective evidence that one has offloaded the MPJs. In his experience, Dr. Clough has rarely found surgical resection necessary for a neuroma of the second intermetatarsal space. He says proper conservative treatment should be sufficient.
Nailing down the exact pathology can be a difficult task, acknowledges Dr. Bouché. He emphasizes the importance of a thorough history and physical exam, diagnostic injections and MRI studies to help validate the clinical impression of an interspace neuroma. To confirm the diagnosis, Dr. Bouché says there should be “congruency” of all of these evaluation methods.