FOOT & ANKLE INTERNATIONAL

Copyright  2005 by the American Orthopaedic Foot & Ankle Society, Inc.

Tibiotalocalcaneal Arthrodesis With a Retrograde Intramedullary Nail:

A Biomechanical Analysis of the Effect of Nail Length

Timothy Noonan, M.D.; Michael Pinzur, M.D.; Odysseas Paxinos, M.D; Robert Havey, M.D.; Avinash Patwardhin, Ph.D.
Maywood, IL

ABSTRACT Key Words: Arthrodesis; Intramedullary Nail; Stress Frac-

ture; Tibia
Background: Fatigue fractures of the tibia have been
observed at the level of the proximal end of the nail after INTRODUCTION
successful tibiocalcaneal arthrodesis with a retrograde
intramedullary device. Materials: To study the effect of
Tibiocalcaneal arthrodesis has gained popularity as
nail length, five matched pairs of cadaver tibiae were
a salvage procedure for severe deformity of the hind-
instrumented with strain gauges and potted in methyl-
foot, most commonly used in the treatment of unstable
methacrylate from a level 3 cm proximal to the distal
Charcot arthropathy of the ankle.4,7,10,12 While standard
medial malleolus to simulate a successful tibiocalcaneal
arthrodesis. A standard length (15 cm) ankle arthrodesis
retrograde intramedullary nailing has been predictable
nail and an identical longer device terminating in the prox- in achieving ankle arthrodesis after trauma, this same
imal tibial metaphysis were inserted in each paired tibia technique is not as universally successful in diabetic
using appropriate technique. The strain of the posterior patients with Charcot arthropathy because of the
cortex of the tibia was recorded under bending moments appreciable bending forces applied to the neuropathic
of up to 50 Nm for each intact specimen after nail insertion ankle, the disease associated osteopenia, and the
and after proximal locking of the nail. The nails were then common presence of morbid obesity.1,5,12,13 Tibiocal-
exchanged between the specimens of the same pairs and caneal arthrodesis commonly is used in this patient
the experiment was repeated to insure uniformity. Results: population to create a more plantigrade foot without
The standard length locked nail increased the principal bony prominences. The loss of motion associated with
strain of the posterior cortex of the tibia at the level of the arthrodesis of both the subtalar and tibiotalar joints
proximal screw holes 5.3 times more than the locked long can apply large bending moments along the length of
nail (353 and 67 microstrains), respectively. This stress the tibia. This biomechanical load theoretically can be
concentration was not observed when the proximal extent transferred to the weakest point in the system, creating a
of the nail terminated within the proximal tibial metaph- stress riser at the site that corresponds to the mechan-
ysis. Conclusion: A successful tibiocalcaneal arthrodesis ically different segments of the tibia: those with and
with a standard length locked intramedullary nail creates
without an intramedullary device (Figure 1).
stress concentration around the proximal screw holes
Standard ankle arthrodesis nails are 15 cm to 20 cm
that may be responsible for the fractures observed clini-
long, placing the proximal tip of the nail approximately
cally. This study supports the use of a ‘‘long’’ retrograde
at the junction of the middle and distal one-thirds of the
locked intramedullary nail for tibiocalcaneal arthrodesis in
patients with systemic or localized osteopenia.
tibia, or approximately at the junction of metaphyseal
and diaphyseal bone. The use of an intramedullary nail
Loyola University Medical Center, Department of Orthopaedics, Maywood, IL that terminates at this level tends to stiffen the distal
tibia, increasing the stress concentration at the junction
Corresponding Author:
Michael Pinzur, M.D. of the nail-tibia composite and the native tibia.
Loyola University Medical Center This study had two objectives. The first was to
Department of Orthopaedics measure the strain along the posterior cortex of the
2160 South First Avenue
tibia at the level of the proximal extent of the nail
Maywood, IL 60153
E-mail: mpinzu@lumc.edu and along the posteromedial aspect of the tibia at a
For information on prices and availability of reprints call 410-494-4994 X226 level corresponding to the placement of the proximal
304

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Foot & Ankle International/Vol. 26, No. 4/April 2005 TIBIOTALOCALANEAL ARTHRODESIS 305

Fig. 2: Potting of the subtalar and ankle joints to simulate arthrodesis.

Identical titanium nails of different lengths were used

Fig. 1: Localized stress reaction at the proximal tip of a tibiotalocal- in the study. A standard commercially-available 15-
caneal arthrodesis nail with associated fracture. cm long titanium ankle arthrodesis nail (EBI, Inc.,
Parsipanny, New Jersey) was compared to an identical
locking screw in a standard intramedullary device. custom nail produced by the same manufacturer. The
The second objective was to compare the mechanical length of the custom nail was selected to terminate
strain along the shaft of the tibia after arthrodesis approximately 5 cm from the proximal articular surface
with a standard length and with a custom-designed within the metaphysis. All of the nails had a diameter of
long intramedullary implant that terminated within the 10 mm. One tibia of each matched pair was prepared for
proximal tibial metaphysis. the standard length nail and the other for the custom nail
instrumentation. A 10-element strip gauge with a length
of 1.59 inches or 4.039 cm. (Measurements Group Inc.,
MATERIALS AND METHODS Raleigh, NC) and a three-element rosette (Tokyo Sokki
Kenkyujo Co., Ltd., Shinagawa, Tokyo) were applied on
Five matched pairs of fresh-frozen cadaver lower the posterior and posteromedial cortex, respectively, of
extremities had simulated tibiocalcaneal arthrodesis each tibia before testing (Figure 3). In all trials, the nail
using retrograde locked intramedullary ankle fusion nails was inserted before application of the strain gauges to
of two different lengths. Before the study, radiographs allow localization of the proximal tip of the nail, and the
were obtained to exclude pathology. The average age proximal screw holes. The strip gauges were secured
of specimens at the time of death was 70.4 ± 6.9 years. with cyanoacrylic adhesive to the posterior cortex of
There were three male and two female specimens. each tibia (Figure 3).8 The rosette gauge was placed
Each specimen was stripped of soft tissues from the adjacent to the proximal interlocking screw hole along
proximal tibia to the talonavicular level of the foot. the posteromedial cortex (Figure 3). The exact positions
Specimen were initially stabilized with a guide wire, of the strain elements were determined with the aid of
positioning the ankle at neutral flexion-extension, 5 the alignment guide for the tibia instrumented with the
degrees of valgus, and 5 degrees of external rotation. standard nail and with fluoroscopy using the nail as a
The nails were inserted using standard clinical plantar guide for the long nail. The manufacturers alignment
insertion sites. The forefoot was amputated at the guide allows placement of the proximal interlocking
talonavicular level to allow the hindfoot to be potted in screws using a guide as opposed to a ‘‘free-hand’’
methylmethacralate inside a special base. The tibia was fluoroscopic guided technique. Using this alignment
included up to a level 3 cm proximal to the distal tip of guide, it was possible to predetermine the precise
the medial malleolus to simulate a successfully ‘‘healed’’ location of the proximal interlocking screw holes along
arthrodesis (Figure 2). By ‘‘potting’’ the entire hindfoot the tibia. Measuring the standard distance between the
within methylmethacralate, the controversy about the proximal screw hole and the tip of the nail, 1.5 cm.,
necessity of a formal talocalcaneal arthrodesis was allowed a determination of the location of the proximal
avoided. A sponge was placed over the nail insertion tip of the nail. The relationship of the strip gauge to
site within the calcaneus to allow easy access to the the nail tip and proximal interlocking screw holes was
insertion portal. precisely determined and duplicated for each specimen

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306 NOONAN ET AL. Foot & Ankle International/Vol. 26, No. 4/April 2005

Load

Posterior Anterior
Fig. 3: Diagram of gauge placement in relation to the intramedullary
nail in each matched pair using the standard and long nail.
10-element
Proximal
Strip Gauge strip gauge
screw hole
1 2 3 4 5 6 7 8 9 10 Standard
three-element length nail
rosette

Proximal
Nail Tip
Screw Hole

Fig. 4: Relationship of 10-element strip gauge to the proximal aspect

of the intramedullary nail.

(Figure 4). The strip gauge spanned the region of the

nail tip and proximal interlocking screw (see Figure 3). Fig. 5: Diagram of the loading apparatus and design.
Mechanical testing of the specimen was done with
an Instron material testing machine (Model 1122 Instron the magnitude of the longitudinal strain induced at the
Inc., Canton, Massachusetts). A nondestructive stiff- levels of the proximal nail tip and the proximal screw
ness test was performed using a force of 500 N that hole (Figure 4).9 Gauges 2, 3, and 4 were grouped for
was applied to the proximal end of the specimen along analysis of the strain along the region of the posterior
the longitudinal axis of the tibia. The potted base of the cortex corresponding to the nail tip (Figure 4). Gauges 7
specimen was secured to an aluminum beam, which and 8 were similarly grouped for analysis of strain in the
extended in an anteroposterior direction. The beam
region of the proximal screw hole (Figure 4). The strain
had an aluminum cylinder attached 10 cm anterior to
data were analyzed using ANOVA and paired t-tests
the center of the distal pot that acted as a contact
adjusted for multiple comparisons. One-tailed p values
point along a load cell during loading (Figure 5).5 The
<0.05 were considered significant.
specimens were loaded to 500 N at a loading rate of
10 mm/minute resulting in a forward bending moment
of 50 Nm. This simulated the forces acting on the tibia RESULTS
at the time of push-off. The strain and load from the
tibia were continuously recorded during testing. Proximal locking of the standard-length intra-
In each matched pair, one randomly selected tibia medullary ankle arthrodesis nail significantly increased
was instrumented with a standard nail and the other the strain adjacent to the proximal screw hole
with a custom ‘‘long’’ nail. The specimens were tested compared to the reamed, noninstrumented tibia (p <
intact, after nail insertion, and after proximal locking with 0.01) (Table 1). The increase in principal strain adjacent
two screws. Proximal locking was accomplished with to the proximal screw holes after instrumentation was
the aiming device available with the standard length 5.3 times greater with the locked standard-length nail
nails and with fluoroscopy for the custom ‘‘long’’ nails. (353 microstrain) than with the locked ‘‘long’’ nail (67
After testing with the initial nail, the nail was removed microstrain) (p < 0.03).
and the tibia was tested with the other length nail. Data The strain along the tensile (posterior) surface of
from the rosette gauges were analyzed to determine the tibia instrumented with the standard-length nail
the principal strain induced in the posteromedial cortex depended on the location adjacent to the proximal
of the tibia at the level of the proximal locking holes.3 portion of the nail. An area of increased strain was
Data from the strip gauges were used to determine identified in the tibia instrumented with the standard

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Foot & Ankle International/Vol. 26, No. 4/April 2005 TIBIOTALOCALANEAL ARTHRODESIS 307

Table 1: Mean principal micro-strain (standard deviation) measured at posteromedial cortex adjacent to
screw hole (three-element rosette)

Strain Location Reamed Tibia Locked Nail Alternate Locked Nail

Distal tibia (Fig. 3A) 2656 (1682) Standard nail 3009∗ (1779) Long nail 1620 (802)
Proximal tibia (Fig. 3B) 97 (284) Long nail 164 (230) Not applicable

∗ Significantly greater than reamed, p < 0.01.

length nail at the level of the proximal locking screw Similar fractures have been reported near the distal
(Table 2). The longitudinal strain on the posterior cortex tip of short intramedullary nails used in the treat-
at the level of the proximal locking screw hole measured ment of intertrochanteric and subtrochanteric femoral
by the strip-gauge elements was significantly (p < 0.01) fractures.2,14 Testing of gamma nails used for proximal
greater in the tibia instrumented with a standard-length femoral fractures demonstrated stress concentration
nail than in the noninstrumented tibia (Table 2). No about the distal tip of the nail instead of at the proximal
difference in strain was detected along the posterior locking screw as in our study; there was no significant
cortex at a region of the tibia corresponding to an difference in stress concentration when the femoral
area between the proximal interlocking screws (gauges nail was locked.14 The use of a longer intramedullary
9 and 10) (Figure 4). The region about the tip of the femoral device was reported to reduce this stress
standard-length nail did not demonstrate a statistically concentration.2,14
significant change in tensile strain when either locked or Lidor et al.9 reported 12 stress fractures of the tibia
unlocked proximally (Table 2). Replacing the standard- after arthrodesis of the ankle or hindfoot. All the stress
length nail with the long nail decreased the principal fractures after ankle arthrodesis were in the middle
(tensile) strain adjacent to the proximal screw hole in and distal aspects of the tibia, and all but one of
the distal portion of the tibia; however, the difference the arthrodeses were fused before the stress fracture
was not statistically significant (1620 compared to 3009 occurred. They suggested that one factor contributing
microstrain, p < 0.10, Table 1). No significant difference to tibial stress fractures after ankle arthrodesis was
was detected in the strain at the level of the proximal the increased bending forces transmitted to the distal
locking screw of the long nail after insertion or locking of aspect of the tibia by the longer lever arm of a
the nail, compared to the reamed, noninstrumented tibia more rigid foot in association with a decrease in the
(97 compared to 164 microstrain, p > 0.05, Table 1). mechanical strength of bone. Thordarson and Chang15
identified a radiographic lucency about the proximal
DISCUSSION aspect of standard ankle fusion nails in some patients,
consistent with the patients’ complaints of pain. In
Tibiocalcaneal arthrodesis with a retrograde locked 12 patients with solid tibiocalcaneal arthrodeses, two
intramedullary nail has gained popularity in the treat- developed nondisplaced stress fractures at the proximal
ment of Charcot arthropathy of the ankle, but the interlocking screws, one at 8 months after surgery and
use of a standard length ankle arthrodesis nail in the other at 15 months. They speculated that cortical
this osteopenic population has been associated with hypertrophy noted in seven of the 12 patients developed
late stress fractures about the proximal aspect of the because of the creation of two stress risers through
nail.11,15 diaphyseal bone leading to stress concentration along

Table 2: Mean longitudinal micro-strain (standard deviation) measured

at posterior cortex for standard length nail (10-element strip gauge)

Reamed Nail (prior to Locked

Strain Location Tibia screw holes) Nail
Nail Tip 1780 (469) 1857 (630) 1988 (626)
Proximal Screw Hole 2083 (386) 2184 (418) 2279 (393)

∗ Significantly greater than reamed, p < 0.01.

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308 NOONAN ET AL. Foot & Ankle International/Vol. 26, No. 4/April 2005

this segment of the distal tibias. Kile et al.7 reported due to one load cycle. Another limitation of this study
that two of 30 patients with tibiocalcaneal arthrodeses was that only limited regions of the tibia could be
developed symptomatic stress reactions. studied. The levels that were studied were based on
The combined use of a strip gauge and rosette initial feasibility testing of various regions along the
allowed localization of the principal strain to the region length of the tibia.
of the posteromedial cortex of the tibia, adjacent to One additional limitation of the study was the elim-
the proximal locking screw during simulated push-off. ination of midfoot motion in the testing. After tibiocal-
Strain was greater in the distal aspect of the tibia than caneal arthrodesis, dorsiflexion and plantarflexion of
proximally along the tibia after simulated ankle and the foot and ankle occur mostly through the midfoot.
subtalar arthrodeses even without instrumentation. This Because several authors have demonstrated that stress
seems to support the speculation of Lidor et al.9 that reactions along the tibia are present after successful
large bending forces transmitted to the distal aspect arthrodesis,9,11,13,15 the ankle and subtalar joints were
of the tibia by the long lever arm contributes to stress ‘‘potted’’ to simulate successful arthrodeses of the
fractures in that region. An additional factor contributed ankle and subtalar joints. However, this removed the
by the locked intramedullary nails was increased motion that the midfoot provides after arthrodesis of
strain adjacent to the proximal locking screw after these joints.
simulation of a successful arthrodesis using a standard
length ankle arthrodesis nail. The standard length nail
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