Metacarpophalangeal Arthroplasty in Rheumatoid Arthritis
Metacarpophalangeal (MP) arthroplasty is the most common
and successful joint replacement surgery of the hand. This
paper will briefly review the anatomy of the MP joint, and the
indications, technique, results and complications of MP arthroplasty.
Although MP implants are occasionally performed for
post-traumatic or osteoarthritic joints, the literature focuses
on patients with rheumatoid or other inflammatory arthritides.
These patients can anticipate deformity correction, improved
function and highly effective pain relief.
The hand is the primary mode of interaction with our
environment. Therefore, even minor alterations of hand and
wrist function resulting from rheumatoid arthritis (RA) affect
the ability to function occupationally, recreationally and in
activities of daily life. A multidisciplinary approach involving
the rheumatologist, hand surgeon, and hand therapist is advisable
in caring for these patients. Because delays in surgical
and non-surgical treatment may lead to further disease progression,
joint destruction and loss of function, early intervention is
imperative. The initial evaluation and subsequent treatment of
each patient's problem are challenging because of the anatomic
complexities of the hand and wrist. However, a strong understanding
of the relevant anatomy and a systematic approach
to patient evaluation allow a logical plan of treatment to be
The normal MP joint is a diarthodial, condylar-type joint.
The metacarpal head has a greater surface area than the base
of the proximal phalanx. The articular surface of the head is
convex and has a wider volar surface. The asymmetry of this
surface accounts for the tightening of the collateral ligaments
when the joint is brought into flexion. This asymmetry also
results in a mobile center of rotation to the MP joint, which
moves volarly with flexion. The normal synovial membrane
of the MP joint is attached around the margins of the articular
cartilage with volar and dorsal capsular reflections. The largest
synovial fold is found on the dorsal neck of the metacarpal10.
The arc of motion of the normal MP joint is described as
neutral to 90 degrees of flexion, although many individuals will
demonstrate variable degrees of hyperextension. Radial and
ulnar deviation is maximized in extension and is decreased with
flexion and the associated tightening of the collateral ligaments.
The MP joint deviates slightly in the ulnar direction with flexion
of the digits.
The joint is stabilized by ligamentous structures. The
collateral ligaments originate on the dorsal aspect of the
metacarpal head - neck junction and insert on the volar aspect
of the proximal phalanx. The collaterals are the primary stabilizers
against varus-valgus and dorsal-palmar stresses. The
volar plate has a membranous attachment on the neck of the
metacarpal and a more fibrous attachment on the base of the
proximal phalanx; it acts as the primary stabilizer against
hyperextension. The flexor tendon sheath, the intermetacarpal
ligaments and the sagittal bands of the extensor hood attach to
the volar plate. The accessory collateral ligaments are located
volar to the collateral ligaments and insert into the volar plate;
they act as stabilizers of the volar plate, as well as secondary
stabilizers against varus-valgus stress.
The interossei and lumbrical muscles exert a flexion force
on the MP joint through their attachments into the extensor
hood and proximal phalanx. The sagittal bands aid in extension
of the MP joint through their insertion into the volar plate, as
well as stabilizing the extensor tendons over the joint itself. The
long flexor tendons can exert a flexion moment on the MP joint
but their insertions on the distal and middle phalanges require
this to occur after interphalangeal joint flexion.
Pathophysiology of Rheumatoid MP Joints
The MP joint is the most common site of involvement in
RA. Destruction of the MP joint in RA begins with a proliferative
synovitis and progressively leads to a volarly subluxated
proximal phalanx with ulnar deviation and destruction of the
articular cartilage. MP joint deformities in RA have been extensively
described. Characteristic changes occur in the articular
surface, soft tissue stabilizing structures and bony supports10,16.
The primary causative factor producing the MP joint deformities
characteristic of RA remains controversial. Zancolli and
others have proposed a dynamic deformity, which exists prior
to articular destruction22. Inflammation of the carpometacarpal
joints exaggerates the spread of the metacarpals and
the tendency for the MP joints to move into ulnar deviation
with flexion. The supination deformity of the carpus leads to a
radial deviation of the metacarpals. The resulting imbalance of
forces on the extensor tendons results in their subluxation off
the metacarpal head. This is facilitated by synovial infiltration
along the collateral ligaments and at their attachments, which
results in stretching out of the radial ligaments, producing
further ulnar deviation and subluxation. The synovial proliferation
within the joint contributes to attenuation of the radial
sagittal bands and facilitates migration of the extensor tendons10,16.
The theory of a dynamic deformity preceding the development
of MP articular changes is not universally accepted,
and some authors feel that changes in the articular surface
are primary. The initial changes seen in articular cartilage
are softening and a loss of normal translucent appearance. A
gradual progression to fibrillation and pitting of the surface of
the metacarpal head occurs, followed by erosions and exposed
bone. Bony erosions correspond to areas of synovial reflection.
Volar erosions tend to be shallower than dorsal ones. Erosions
in any area have the potential to penetrate through the cortical
bone, although this is less common volarly. In advanced cases,
the erosions can coalesce circumferentially around the metacarpal
neck. Erosions of the proximal phalanx occur later in the
disease and tend to involve a circumferential margin around
the base of the phalanx10.
The capsular laxity of the MP joints that allows radial-ulnar
deviation and flexion-extension motion makes subluxation/
dislocation common sequelae of synovitis. When capsular laxity
is combined with extensor tendon subluxation, joint deformity
progressively leads to a fixed, volarly subluxated proximal
phalanx with ulnar deviation. Attempts at finger extension
lead to ulnar deviation. Additional ulnar deviation forces come
from deformity of the wrist and tenosynovitis of the flexor
tendons resulting in ulnar displacement of the flexors. With
progressive subluxation the radial sided structures stretch and
the ulnar ligaments and intrinsic muscles shorten. The fixed
flexion deformities result in the inability to open the hand to
grasp large objects and difficulty in fine manipulation of objects
between the index and long fingers and the thumb.
Nalebuff and Millender have classified deformity of the MP
joint in RA11. Stage I disease is characterized by MP synovitis
with the ability to fully extend the joint, and little ulnar
deviation or articular changes. Patients are managed medically
for the synovitis, with splinting and/or corticosteroid injections
for symptomatic relief. Night splints that hold the MP
joints in extension and correct ulnar deviation are frequently
Stage II is marked by the development of early erosions.
Pain is generally the chief complaint. The extensor tendons
show a tendency to move towards the web spaces. An extensor
lag commonly exists, but flexion is well preserved. Clinical
intervention focuses on maximizing medical management.
Surgical intervention is infrequently performed, but could
include synovectomy and soft tissue balancing. Synovectomy
is not thought to alter the long-term prognosis of the disease
but is widely accepted for alleviating local symptoms. Prior
to undertaking soft tissue realignment, the surgeon must
consider the adjacent joints and the mechanical effects on the
MP. The incision for a Stage II procedure is the same as that
utilized for arthroplasty should further surgery be necessary.
Some surgeons consider crossed intrinsic transfers to the radial
lateral band for significant ulnar deviation.
Stage III disease is characterized by advancing joint
destruction and increasing deformity. These patients frequently
have substantial PIP disease. The surgical decision
is whether arthroplasty or tendon centralization and synovectomy
is appropriate. The patient's level of pain and the function
of the affected hand typically guide this decision.
Stage IV disease is marked by fixed subluxation and
destruction as seen on radiographs. By this stage, silicone
implants are widely considered the treatment of choice, and
decision-making focuses on the options available for the other
joints. However, in a young patient with a functional range
of motion of the MP joint (an active arc of motion of 60 to
70 degrees), the surgeon must determine whether surgical
intervention is indicated, as there is unlikely to be functional
improvement. Examination of the wrist and PIP joints must be
performed, as changes in these areas are more common with
advanced disease and may need to be surgically addressed prior
to performing an MP arthroplasty3,16.
Evaluation of the rheumatoid patient with involvement
of the MP joints requires an assessment of the global function
of the extremity and in particular any deformities of adjacent
joints. Adjacent joint deformity and subsequent progression
may contribute to the ultimate success or failure of any procedure
performed in the MP joints. Progressive deformity of
the wrist, in particular, may predispose MP arthroplasty to early
recurrent ulnar deviation. A systematic framework, which
divides the hand and wrist into four anatomic regions, should
be followed in examining a deformed hand and wrist.
First, the wrist should be evaluated for localized areas of pain, tenderness
and swelling indicative of synovitis or tenosynovitis. Changes
in range of motion over time are important when evaluating disease
progression. Next, the thumb joints--carpometacarpal (CMC),
metacarpophalangeal (MP), and interphalangeal (IP)-- are examined.
Deformity and active and passive ranges of motion are all checked.
Third, the index through small fingers are evaluated for swelling,
deformity and range of motion at the MP joint. Lastly, the proximal
interphalangeal (PIP) and distal interphalangeal (DIP) joints are
assessed for articular destruction and tendon imbalance. (Figure 1)
Rest, exercise, splinting and corticosteroid injections play a
critical role during early and late stages of the disease. Inflamed,
painful joints will commonly respond to rest to diminish acute
synovitis. Diseased joints require use to prevent worsening
contractures, as active motion is needed to maintain tendon
gliding and muscle tone. In general, short frequent periods of
exercise are preferable to longer periods that have the potential
to aggravate existing inflammation. A hand therapist is invaluable
to achieve the appropriate balance and monitor activity.
Patients are commonly treated with resting and dynamic
splints. Resting splints are effective in relieving pain yet allow
many functional activities. Dynamic splints provide slow, constant
stretching to help alleviate deformity. Corticosteroid injections
are utilized to lessen synovitis and tenosynovitis and are
commonly used for carpal tunnel syndrome, extensor tenosynovitis
and for individual joints refractory to medical treatment.
While serious complications are uncommon, tendon ruptures
may be caused by frequent or repeated steroid administration.
Thus, steroid injections should be limited to two or three times
annually. Any joint or tendon sheath in the hand with synovitis
prompting repeated steroid injection may benefit from surgical
The history of MP joint replacement is heavily dependent
upon the work of Albert Swanson, which was first reported in
196617. The silicone rubber implants used in MP arthroplasty
differ in their fixation, articulation and motion from
the prostheses commonly used in larger joints. The role of the
implant, according to Swanson, is not to function as a true
prosthesis, but to serve as a spacer to maintain the joint in
alignment after a resection arthroplasty is performed18. The
implant provides enough stability in the early post-operative
period to mobilize the joint. However, the contribution of the
implant to joint motion is debated. These prostheses have been
described as "dynamic spacers18." The implant promotes the
development of a fibrous capsule, adapted to a functional range
of motion determined by the post-operative mobilization.
Swanson has termed the development of this fibrous capsule
the "encapsulation process18."
Silastic MP implants are inserted without an attempt to
achieve rigid fixation. The encapsulation process itself is the
definitive fixation of the implant. A small amount of pistoning
of the intramedullary stem of the implant occurs3. Attempts
at more rigid fixation of these implants have resulted in early
fracture and clinical failures. The pistoning or gliding of the
implant within the medullary canal adds to the range of motion
achieved by the arthroplasty, in addition to dispersing the forces
of motion along the implant-bone interface16,18.
The technique for MP arthroplasty has been extensively
described2,4,5,8,18. A dorsal transverse incision is used at
the level of metacarpal head-neck junction. The dorsal veins
are preserved to the extent possible. The extensor mechanism
is exposed and a longitudinal incision is made in the
extensor hood. Swanson and most other authors make this
incision through the attenuated ulnar sagital band, although
Beckenbaugh and Lindscheid recommend preserving the ulnar
hood if possible and incising the radial aspect of the extensor
mechanism3,18. The capsule is then incised longitudinally
and the neck of the metacarpal is exposed. A soft tissue release
is necessary to relocate the phalanx and to allow preparation
of the bony structures for insertion of the component. The
collateral ligaments are released at their origin and the contracted
ulnar intrinsics, including the abductor digiti minimi,
are released. The flexor digiti minimi is preserved, as the small
finger typically has the most difficulty achieving active flexion
post-operatively. Some surgeons prefer not to release the ulnar
intrinsic to the index finger in an attempt to preserve the function
of the first palmar interosseous muscle for pulp to pulp pinch.
The metacarpal head is then removed along with capsular
attachments after transecting the neck with a saw, rongeur or
drill. The level of resection is just distal to the origin of the
now reflected collateral ligaments. Hypertrophic synovium
within the joint capsule is then removed3,18. Preparation
of the medullary canal of the metacarpal is performed with
hand reamers. Swanson uses a specially designed burr with a
smooth tip to lessen the chance of cortical perforation. There
is evidence that over-reaming of the canal is associated with
periprosthetic bone loss post-operatively; therefore, reaming is
minimized in both the metacarpal and proximal phalanx. After
reaming, a trial prosthesis is selected. An effort is made to fit
the largest size without applying undue force. An appropriately
sized prosthesis should fit snugly while the transverse midportion
of the implant rests against the cut surface of the bone18.
The proximal phalanx is prepared by making a perforation
in the subchondral bone in line with the center of the medullary
canal. The hole is enlarged to accept a rectangular prosthesis
with a rasp or burr. The index finger may be held in a
slightly supinated position while rasping to improve tip pinch.
After preparation and reaming of the selected, trial prostheses
are once again inserted to ensure proper fit. With placement of
a properly sized trial, no subluxation of the joint should occurr
and the implant should fit snugly into both canals18.
To improve the durability of the implants, some authors
have suggested the use of implants with titanium grommets.
In theory, the titanium protects from silastic wear. However,
there is little clinical data documenting any benefit, and the
data from animal experiments is inconclusive13. Some
surgeons reserve the use of grommets for cases with extensive
erosion of the dorsal aspect of the proximal phalanx to achieve
a more stable construct.
Prior to insertion of the actual prosthesis, soft tissue
reconstruction of the radial ligament complex must be considered.
This is accomplished with the proper collateral ligament,
unless it is severely attenuated. It is reattached with nonabsorbable
suture through holes in the metacarpal neck and
imbricated as necessary. If the collateral ligament is deficient,
an alternative radial ligamentous reconstruction has been
described with the volar capsule and half of the volar
plate attached to the origin of the collateral ligament3,16,18.
Kirschenbaum and Schneider have described good long-term results
without a radial reconstruction. (Figure 4)
The bony surfaces are then irrigated and prepared
for implantation. A socalled "no-touch" technique
is used with smooth forceps so as not to injure the surface
of the silicone rubber, as implant fracture has been
related to propagation of surface defects. The implant
is first inserted into the metacarpal and then with flexion and
distraction the distal end is placed into the phalanx. The radial
reconstruction is tied down after placement of the implant, and
the capsule is closed. The extensor tendon is centralized and
the radial sagittal bands are reefed. The skin is closed with
interrupted sutures over a subcutaneous drain. A bulky dressing
is applied and the hand is splinted with the MP joints in
extension to protect the soft tissue reconstruction16,18.
The traditional post-operative therapy protocol begins
within one week of surgery. The patient is fitted with a dynamic
splint holding the MP joints in extension and neutral to radial
deviation. A static resting splint is also fabricated. The patient
is encouraged to actively flex the MP joints in a controlled fashion
to protect the extensor realignment and prevent prosthetic
dislocation. The patient is weaned from the dynamic splint at
six weeks post-operatively but static splinting is continued at
night for three to four months20.
An alternative postoperative protocol has recently been
proposed14. The patients are placed in a hand-based cast
with the MP joints in extension and 10-15 degrees of radial
deviation. The wrist and distal joints are left free. The cast is
removed after 5 weeks and patients are begun in a therapy program
of active and passive motion with a static nighttime splint
for an additional six weeks. This protocol has demonstrated
comparable results in one large series from a single surgeon
and offers a much simpler rehabilitation protocol for patients
Results and Complications
The silastic implants used in MP arthroplasty function
differently than those used in the more common large joint
replacements. MP silastic arthroplasties are not fixed to the
skeleton and patients have motion between the implant and the
bones as well as within the implant. Attempts at engineering
MP arthroplasties similar to larger joint replacements continue,
but they are not widely accepted at this time. The literature on
these MP total joint replacements is limited and demonstrates
results that are not convincingly superior to silastic arthropasty
for most patients with RA. In addition, dislocation of these less
constrained implants can occur as a result of the extensive soft
tissue attenuation/destruction in RA.
The results after MP silastic arthroplasty are well-documented.
Overall, function is substantially improved in appropriately
selected patients. The variables reported in the literature
include range of motion, ulnar deviation, pain relief and
patient satisfaction. Realistic expectations are important, as
the arthroplasties are not expected to achieve a full range of MP
motion. Patients with substantial extensor lag or ulnar deviation
preoperatively will only have a small increase in the arc of
motion, but the arc will be in a more functional position. Key
and tip pinch will also be improved as the index is brought over
into a radial position. Reported post-operative arcs of motion
vary from 38 to 60 degrees1,2,4,5,7,8,18. Extension lags also
vary from 9 to 22 degrees1,2,4,5,7,8,18. Loss of motion over
time also may occur, as Bierber reported a loss of 12 degrees of
active motion at an average of 5 years of follow-up4.
Ulnar deviation is reliably corrected, although there is a
tendency for some ulnar drift to recur with long-term followup.
The correction of deformity has been documented as one of
the major contributors to patients' subjective sense of improvement.
Correction within a few degrees of neutral is reported in
most series. Recurrent ulnar drift has been reported in up to
43% of patients, however, the recurrent deformities reported is
less than 20-30 degrees in most series1,2,4,5,7,8,18.
Pain relief is inconsistently documented in follow-up
studies of MP arthroplasty, although clinical experience suggests
that it is consistent. Kirschenbaum reported that of 144
arthroplasties in 36 hands, none complained of pain. Bieber
reported that only 20% of patients in their series reported pain
as a pre-operative concern4,8. Beckenbaugh reported recurrence
of pain in 2 percent of patients at an average follow-up of
32 months2. Patient satisfaction with the procedure is generally
high, with the majority of patients in most series reporting
they would undergo the procedure again.
The patient's subjective appraisal of outcome has been
investigated for its relationship to deformity, strength, range of
motion, pain relief and other traditional parameters of success.
Notably, the strongest determinant of patient satisfaction was
with appearance and correction of deformity. Pain relief was
also found to be important, but the other traditionally examined
parameters (motion, strength etc.) were not found to have a
statistical correlation9. (Figure 2)
Silicone rubber MP joint implants generally have a low
rate of complications1,2,4,5,7,18. Several other types of MP
prostheses have a higher rate of long-term complications1.
Foliart has published an extensive review of the literature on
complications of Swanson finger joint implants7. The most
frequently reported complication was extensive change in the
bone surrounding the implant. This complication was found
in 4% of silicone rubber implants7. Swanson has extensively
studied the changes in bone morphology19. Metacarpal midshaft
cortical bone consistently decreased post-operatively in
this study, and the length of metacarpals with implants in place
decreased by an average of 9%19. Bones remodeling also
resulted in thickening of the bony surfaces at the metacarpal
and phalangeal metaphysis while maintaining the shape of the
cut end of the metacarpal19.
Foliart found implant fracture in 2% of reported cases7.
However, the rate of implant fracture varies form 0%4 to
38%2 and may depend on how extensively the investigator
looks for radiographic evidence of fracture1,2,4,5,8,18. Many
authors report that the majority of patients with fractured
implants have acceptable function and do not require revision.
The low morbidity of fractured prosthesis has been related to
the function of the implant as a spacer rather than as an articulated
prosthesis1,2,4,5,8,18. Several changes have been made
in the implants to address this problem. The originally used
silicone rubber 372 has been replaced by "high performance"
(HP) silicone rubber. In vitro investigation demonstrates
improved resistance to fracture and tear propagation with the
newer silastic. Studies of HP implants only have shown fewer
fractures when compared to historical studies, although to our
knowledge no controlled trials have been undertaken to evaluate
this. (Figure 3)
Infection was noted in 0.6% of reported implants by Foliart7.
Most series, including Swanson's, report a rate between 0.1
and 1%1,2,4,5,8,12,18. Millender and Nalebuff have published
a detailed report on infection after silicone arthroplasty in the
hand. All of Millender's infections presented within 8 weeks
of implantation. Staphylococcus Aureus was the most common
organism isolated and most of the prostheses ultimately
required removal, and an average of two weeks of antibiotic
Particulate synovitis and silicone induce lymphadenopathy
have received substantial attention. Both of these
complications were recorded in less than 0.1% of reported
cases by Foliart7. Synovitis in MP implants occurred almost
exclusively in fractured implants or in implants with substantial
signs of wear at removal. Four patients with lymphadenopathy
and silicone rubber implants have been reported who developed
non-Hodgkin's lymphoma. All four were in rheumatoid
patients with a concomitant 10-fold increased risk over the
general population of developing lymphoma7.
A variety of alternatives to silastic flexible implants have
been proposed in the more than 30 years since they came in
widespread use, but none have gained wide acceptance. (Figure 6)
Current alternatives include implant designs more analogous
to joint replacements used in larger joints. (Figure 5A and B)
Specific differences from silastic arthroplasty include rigid
fixation and the use of two distinct components. There are
currently both cemented and cementless components available
on the market. While these implant have been implanted and
evaluated to a certain degree in the literature, further investigation
is warranted to establish the indications, contraindications,
results and longevity of these types of implants in relation to
silastic MP arthroplasty for patients with RA.
Treatment of the arthritic rheumatoid MP joint requires
consideration of the degree of compromise, as well as a thorough
understanding of the anticipated outcome of the options
for intervention. Silicone MP arthroplasty is one of the more
successful operations performed in these patients when it is
applied at the appropriate stage. The patient can anticipate a
reversal of deformity, an active arc of motion of 40 to 50 degrees
in a functional position and effective pain relief. Subjectively,
patients report satisfaction with the correction of deformity and
pain relief. Although MP arthroplasty is a successful procedure,
problems do exist. Recurrence of a mild ulnar drift deformity
occurs in a substantial percentage of patients. Implant fracture
remains a concern, although the incidence of this problem has
probably been reduced with the development of high performance
silicone rubber. Longevity and reliable function beyond
ten years has yet to be documented. Silicone arthroplasty provides
an important method for the hand surgeon to improve the
function of patients with severe MP disease. Future advances in
implant technology and surgical technique will need to address
existing problems to allow MP arthroplasty to become a more
successful and widely applicable operation.
Please address correspondence to:
Philip E. Blazar, M.D.
Assistant Professor in Orthopedic Surgery
Harvard Medical School
Attending Physician, Department of Orthopaedic Surgery
Brigham and Women's Hospital
75 Francis Street
Boston, MA 02115
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