How To Address Key Biomechanical Issues With Second MPJ Injuries
Injuries to the second metatarsophalangeal joint (MPJ) can be challenging to treat. Our expert panelists discuss predisposing factors to injury and review pertinent biomechanical considerations. They also discuss conservative treatment options, including variations of orthotic therapy and modifications that they have employed in clinical practice.
Q: What are the predisposing factors (gender, foot type, activity, etc.) that are associated with injuries to the second MPJ?
A: Second MPJ injuries may have a variety of etiological causes, according to Kevin Kirby, DPM. He notes the most common causes are increased second metatarsal length, decreased dorsiflexion, first ray stiffness (such as increased dorsiflexion compliance of the first ray), obesity, thin-soled, high-heeled shoes, excessive subtalar joint pronation and plantar metatarsal fat pad atrophy. In addition, Dr. Kirby says athletic activities, such as running and jumping activities, which increase the loading forces on the forefoot, may lead to an increased risk of second MPJ injuries.
As James Clough, DPM, says, the second MPJ is prone to injury whenever the foot structure faces increased medialization of weightbearing forces. He says this could be caused by a myriad of biomechanical abnormalities including an increased Q angle and pronation of the rearfoot past the vertical position. A Morton’s foot type is also a significant factor that predisposes one to pronation, according to Dr. Clough. He also cites second MPJ overload due to the length discrepancy that exists between the first metatarsal and the second metatarsal.
Dr. Clough says second MPJ injuries are also common among people who walk only short distances during the day as they develop an apropulsive gait pattern due to a lack of active engagement of the windlass mechanism. He adds that second MPJ injuries can also affect people who stand in one spot for long periods of time and never use the foot dynamically. Dr. Clough says both types of patients are predisposed to second MPJ injuries as the first metatarsal does not plantarflex into the ground to accept normal weight distribution. He notes that older people who have a shuffling gait because of poor proprioceptive issues are significantly predisposed to second MPJ pain.
Richard Bouché, DPM, sees an equal distribution of males and females with second MPJ instability in all patient groups, including sedentary, active and athletic patients. Patients over age 60 seem to experience these injuries more commonly due to attrition, according to Dr. Bouché. He occasionally sees traumatic or iatrogenic causes. Dr. Bouché says the most common iatrogenic cause is steroid injections that use triamcinolone (Kenalog, Bristol-Myers-Squibb). Patients who seem to be prone to this problem include those with a moderate to severely pronated foot, those with flexible forefoot equinus and/or patients with rheumatic disease, according to Dr. Bouché.
Dr. Clough says other predisposing factors include high heels that increase forefoot overload and shoes that are too rigid in the forefoot as they do not allow for proper bending of the first MPJ.