Orthotics Q&A: How To Address Key Biomechanical Issues With Second MPJ Injuries

Podiatry Today
Orthotics Q&A:
How To Address Key Biomechanical Issues With Second MPJ
Injuries
- Guest Clinical Editor: Douglas Richie Jr., DPM
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.
Q: What biomechanical factors are associated with the pathomechanics of injury to the
second MPJ?
A: Dr. Clough maintains that injury to the second MPJ is first and foremost a problem with
insufficiency of the first ray. If the windlass mechanism is not engaging properly and the first
metatarsal is not plantarflexing into the ground to accept adequate weightbearing, Dr. Clough says
then the second metatarsal will be overloaded.
Not only is the first ray capable of excessive dorsal displacement but Dr. Clough says it is also
capable of significant plantar displacement with proper foot function. If the first metatarsal head
remains in a dorsally displaced position due to inadequate function of the first MPJ, he says this
results in the inevitable overload of the second MPJ.
“This of course is the case with functional hallux limitus, which is present in a great number of
insufficiency of the first ray. If the windlass mechanism is not engaging properly and the first
metatarsal is not plantarflexing into the ground to accept adequate weightbearing, Dr. Clough says
then the second metatarsal will be overloaded.
Not only is the first ray capable of excessive dorsal displacement but Dr. Clough says it is also
capable of significant plantar displacement with proper foot function. If the first metatarsal head
remains in a dorsally displaced position due to inadequate function of the first MPJ, he says this
results in the inevitable overload of the second MPJ.
“This of course is the case with functional hallux limitus, which is present in a great number of
feet in clinical practice,” says Dr. Clough. He says research has shown that hallux limitus is present
in 62 percent of asymptomatic feet and adds that the condition is present in close to 80 percent of
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the feet he sees in clinical practice.
“It is a pervasive problem that needs to be dealt with for effective therapeutic outcomes,”
emphasizes Dr. Clough.
Dr. Bouché says one must consider biomechanical factors such as ankle equinus, a
hypermobile medial column with or without bunion deformity, and/or a prominent second metatarsal
that is either long or plantarflexed.
Dr. Kirby says the vast majority of second MPJ injuries are actually injuries to the plantar plate,
which is a fibrocartilaginous structure plantar to the lesser MPJs and which is continuous with the
plantar fascia. He explains that the plantar plate is subject to large magnitudes of tensile forces from
the plantar fascia and is also subject to large magnitudes of compressive forces from ground
reaction force (GRF) on the forefoot during weightbearing activities. This greatly increases the risk of
the plantar plate developing partial or complete tears within its structure, according to Dr. Kirby.
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.
Q: What is your protocol for conservative treatment of suspected injury to the plantar plate of
the second MPJ?
A: All three panelists cite the use of icing. Dr. Kirby suggests icing 20 minutes twice a day directly
plantar to the second MPJ. He says this can significantly reduce plantar edema in the MPJ, which in
turn can help reduce the compression forces on the plantar plate during weightbearing activities.
Dr. Kirby also cites plantarflexion taping of the digit to relieve the tensile forces on the plantar
plate. This allows the injury to heal faster and leads to reduced pain with weightbearing, according to
Dr. Kirby. Dr. Bouché concurs. He also suggests using digital spacers if there is any transverse
plane component to the deformity. Dr. Bouché also recommends using a metatarsal binder or corset
to stabilize the medial column by decreasing the first and second intermetatarsal angle.
In order to allow normal healing, Dr. Kirby says it is essential to use modified over-the-counter
foot orthoses or prescription foot orthoses that are designed to reduce the ground reaction forces
plantar to the second MPJ.
For Dr. Bouché, orthotic treatment options also include OTC or custom orthoses to control
excessive pronation, forefoot extensions with the second metatarsal cutout and/or a metatarsal
“cookie,” and a rigid rocker-soled shoe to offload the forefoot. Depending on the stage of the
problem, Dr. Bouché says NSAIDs or a walking boot can be helpful in the acute/subacute stages.
Dr. Kirby also recommends four to six weeks of a boot walker brace or a below-knee immobilization
cast, which may be necessary to rest the injured plantar plate and to permit healing if other methods
have not prevailed.
Conservative treatment for offloading of the second MPJ must be the first and foremost
objective, emphasizes Dr. Clough. He says one can only accomplish that by restoring normal motion
of the first MPJ and properly engaging the windlass mechanism of the foot structure.
If a functional hallux limitus is not properly engaging the windlass mechanism, he says the first
metatarsal will not displace into the ground as part of dorsiflexion of the first MPJ and therefore, the
first metatarsal will not accept adequate weightbearing into propulsion. Dr. Clough explains that
when the foot goes into propulsion with a very unstable foot structure and an unstable first ray, the
second MPJ will overload since the anatomy of the foot dictates that the second metatarsal will not
be able to displace dorsally under weightbearing forces as well as the first metatarsal is capable of
doing.
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Dr. Clough notes the Cluffy Wedge is often a very effective addition to a shoe insole or OTC
device before one considers custom orthotic therapy. As he explains, the wedge will offload the
second MPJ by increasing dorsiflexion of the first MPJ and improving first metatarsal plantarflexion.
After offloading the second MPJ, he says physical therapeutic modalities may be of some benefit.
Dr. Clough warns that under no circumstances should one inject corticosteroids since it will further
weaken the soft tissues and aggravate the condition.
Q: In terms of orthotic therapy, what are the specific orthotic requirements and prescription
criteria for offloading the second MPJ?
A: One should use a balanced/negative impression cast and cast out supinatus deformity if it is
present, according to Dr. Bouché. In addition, he advises using a deep heel seat, a moderate medial
arch fill, no lateral arch fill (to capture the lateral arch fully), a forefoot extension with a sub-second
metatarsal cutout and/or metatarsal cookie. One may use additional strategies depending on the
severity of the pronated foot deformity. Dr. Bouché says options may include a medial skive, inverted
orthoses or a medial extended rearfoot post.
For the past 15 years, Dr. Kirby has used the following orthosis modifications to achieve very
good therapeutic results in treating second MPJ pathology. He uses a 3/16-inch polypropylene plate
with a standard rearfoot post, minimal medial arch fill and a 2 to 3 mm medial heel skive in the
orthosis to increase the supination forces on the foot and redirect ground reaction force (GRF)
toward the lateral forefoot. He says one should also make the anterior orthosis edge with an abrupt
3/16 inch drop-off or an “internal metatarsal bar” to reduce the GRF on the metatarsal heads.
In addition, Dr. Kirby notes that clinicians should also order the anterior orthosis edge so the
orthosis shell parabola extends distally to all of the metatarsal necks and the orthosis is much longer
under the distal second metatarsal shaft. He calls this a “capsulitis modification.” He uses a full
length, 1/8-inch neoprene topcover along with a 1/8-inch korex forefoot extension plantar to the first,
third, fourth and fifth metatarsal heads. Sometimes he combines this with a metatarsal pad
sandwiched between the top cover and orthosis shell to facilitate further reduction of the GRF on the
second MPJ.
During the casting of the orthotic, Dr. Clough advocates maximum dorsiflexion of the first MPJ to
plantarflex the first ray and allow the first ray to bear weight when one is dispensing the orthotic. As
he explains, this maneuver will reduce forefoot supination and eliminate the need to correct an
inverted forefoot deformity. Intrinsic or extrinsic balancing of a forefoot supination will always result in
jamming of the first MPJ and he says one should avoid this in all situations in which this deformity is
reducible. Minimal arch fill is necessary to slow down any eversion velocity over the foot structure
and provide pressure to the base of the first metatarsal, according to Dr. Clough.
Re-establishing the first ray function is critical for an orthotic to be effective and Dr. Clough feels
applying a Cluffy wedge is a good solution as it pre-stresses the hallux in dorsiflexion and allows
proper first MPJ motion to occur. He says this reliably overcomes a functional hallux limitus. As the
first MPJ dorsiflexes, he says the first metatarsal plantarflexes and helps offload the second MPJ.
Other orthotic modifications like a reverse Morton’s extension or a kinetic wedge rely on
increased pressure underneath the lesser metatarsals and decreasing weightbearing underneath the
first metatarsal to improve the range of joint motion for the second MPJ, says Dr. Clough. He notes
this is counterintuitive if one is trying to decrease weightbearing on the second MPJ. Further, he
says it is critical to establish normal first metatarsal weightbearing pressure to overcome second
MPJ forefoot pathology but still enable the coupling mechanism of rearfoot supination to occur in a
timely fashion.
Dr. Bouché is a Staff Podiatrist at The Sports Medicine Clinic in Seattle. He is a Fellow of the
American Academy of Podiatric Sports Medicine, a Diplomate of the American Board of Podiatric
Surgery and a Fellow of the American College of Foot and Ankle Surgeons.
Dr. Clough in practice at the Foot and Ankle Clinic in Great Falls, MT. He is the inventor of the
Cluffy Wedge. He is a Diplomate of the American Board of Podiatric Surgery. He can be reached at
jclough@sofast.net
Dr. Kirby is an Adjunct Associate Professor in the Department of Biomechanics at the California
School of Podiatric Medicine at Samuel Merritt College. He is the Director of Clinical Biomechanics
at Precision Intricast Inc.
Dr. Richie is an Adjunct Associate Clinical Professor in the Department of
Applied Biomechanics at the California School of Podiatric Medicine. He is in
private practice in Seal Beach, California. He can be reached at drichiejr@aol.com
Douglas Richie
Jr., DPM
Reference
1. Payne C, Chuter VC, Miller K. Sensitivity and specificity of the functional hallux limitus test to
predict foot function. JAPMA 92:269, 2002.
Podiatry Today - ISSN: 1045-7860 - Volume 21 - Issue 4 - April 2008 - Pages:
40 - 45