Strain measurement in lateral ankle
ligaments MARK R.
COLVILLE,* MD, RICHARD A. MARDER, MD, JOHN J. BOYLE, MD, AND BERTRAM ZARINS, MD
From the
Orthopaedic Service, Massachusetts General Hospital, Boston, Massachusetts posterior tibiofibular ligament
ABSTRACT
tears with extreme dor-
siflexion. We measured strain in the lateral ligaments of 10 human cadaver ankles while moving the ankle joint and applying stress in a variety of ways. We studied the anterior talofibular, calcaneofibular, posterior talofibular, anterior tibiofibular, and posterior tibiofibular ligaments. Strain measurements in the ligaments were recorded continuously while the ankle was moved from dorsiflexion into plantar flexion. We then repeated measurements while applying inversion, eversion, internal rotation, and external rotation forces. Strain in the anterior talofibular ligament increased when the ankle was moved into greater degrees of plantar flexion, internal rotation, and inversion. Strain in the calcaneofibular ligament increased as the talus was dorsiflexed and inverted. These findings support the concept that the anterior talofibular and calcaneofibular ligaments function together at all positions of ankle flexion to provide lateral ankle stability. We measured maximum strain in the posterior talofibular ligament when the ankle was dorsiflexed and externally rotated. The strain in the anterior and posterior tibiofibular ligaments increased when the ankle was dorsiflexed. External rotation increased strain in the anterior tibiofibular ligament and decreased strain in the posterior tibiofibular ligament. Based upon strain measurements in the lateral ankle ligaments in various ankle joint positions, we believe the anterior talofibular ligament is most likely to tear if the ankle is inverted in plantar flexion and internally rotated. Theoretically, the calcaneofibular ligament tears primarily in inversion if the ankle is dorsiflexed; the anterior tibiofibular ligament tears in dorsiflexion, especially if combined with external rotation; and the
Ankle ligament sprains are common injuries. The roles that various ankle ligaments play in resisting excess forces remain unclear, however. Successful repair of torn ligaments and reconstruction of chronically unstable ankles require a clear understanding of the function of the ankle ligaments. Leonardl° and Anderson and LeCocq’ studied lateral ankle ligaments at surgery and during anatomical dissections. Several investigators have measured talar displacement and rotation after selective sectioning of various ligaments, but often with conflicting results.3, 5, 9, m> 13-15, Zo Others used radiographic techniques to measure changes in ankle stability after various injuries or experimentally induced ligament disruptions.8,16 The problem with ligament cutting studies is that ankle biomechanics are altered and the findings are not derived from measurements of dynamic relationships of the various ligaments. Shybut et a1.19 measured forces in intact ankle ligaments using buckle transducers. They found that there was little tension in lateral ankle ligaments through most of the range of normal ankle motion. Kennedy et al.,s Arms et al.,2 and Monahan et a1.12 used mercury-filled strain gauges to measure strain in intact knee ligaments. They measured strain without altering the ligament characteristics or joint mechanics. The purposes of this study were to measure strain in intact ankle ligaments during dorsiflexion and plantar flexion and to measure changes in strain when the ankle was inverted, everted, internally rotated, and externally rotated.
MATERIALS AND METHODS
Specimens *
Address correspondence and repnnt requests to: Mark R Colvdle, MD, Division of Orthopedics and Rehabilitation, The Oregon Health Sciences University, 3181 S W Sam Jackson Park Road, Portland, OR 97201.
Ten human ankles were tested. Three specimens were from fresh cadavers and seven had been frozen for less than 1 196
197
month. The average age of the specimens was 64 years, the range being 28 to 79 years. Most of the amputations had been performed because of ischemic vascular disease. The skin and soft tissues were removed and the ligaments and bones were left intact. If the specimen came from a below-knee amputation, the fibula was stabilized to the tibia using a screw placed as proximally as possible in order to minimize the effect of the screw on normal joint mechanisms. The screw held the fibula in its proper orientation to the tibia and maintained normal tension in the interosseous membrane. In above-knee amputation specimens, the knee was disarticulated and the proximal tibiofibular joint was left intact. The forefoot was transected through the metatarsal bones.
Mounting Three smooth Steinmann pins each 5 mm in diameter were drilled transversely through the tibia at a level approximately 15 cm above the ankle joint. The pins were secured to each other using modified Hoffman clamps. A 5 mm diameter pin was drilled into the anterior talus from an anterior to posterior direction passing through the space between the first and second metatarsal bones. This pin transfixed the first cuneiform and navicular bones and passed into the talus through its center of rotation. Two Schanz screws 6 mm in diameter were drilled across the subtalar joint passing through the calcaneus into the talus parallel to the longitudinal axis of the tibia. Subtalar joint motion was eliminated so that strain in the calcaneofibular ligament could be measured in relation to ankle joint motion only. The anterior screw passed through the center of rotation of the talus. This fixation eliminated motion at the subtalar joint.
Inc., Montreal, Canada). This computerized system enabled to measure displacements using an electrogoniometer and to measure forces that were applied using a force plate. The Genucom computer was also interfaced with the Apple IIC computer to allow simultaneous display of data, such as strain versus flexion angle and joint force. The anterior talofibular, calcaneofibular, and the long fibers of the posterior talofibular, anterior tibiofibular, and posterior tibiofibular ligaments were studied. After the strain gauges were attached to the ligaments, the ankles were moved through a full range of motion several times. The gauges were rechecked to be sure no slippage had us
occurred. The ankles
were
moved from 20° of dorsiflexion
plantar flexion while no versional or rotational forces were applied. Strain was measured continuously in each ligament through this range of motion. Strain was then measured continuously in each ligament through the range of motion while moments of 3 Nm of internal rotation, external rotation, inversion, and eversion were applied to
to 30° of
the talus.
Although a weightbearing model would have been preferable, the constraints of our testing apparatus did not allow us to apply a physiologic load across the ankle joint while measuring strain. RESULTS Strain in the anterior talofibular ligament (Fig. 1) progressively increased as the ankle was moved from 20° of dorsiflexion to 30° of plantar flexion. The greatest rate of increase
Instrumentation
Mercury-filled Silastic strain
gauges
(Parks Medical Elec-
used. The inner diameter of each was 0.30 mm and the outer diameter was 0.64 mm. The electrical resistance of the strain gauges, which changed as a function of length, was processed using an eight-channel metering system. This system produced a linear voltage output for strains between 0% and 20%. Calibration curves for each strain gauge were made at 100 jAm increments to confirm that each gauge had a linear output. The meter was interfaced with an Apple IIC computer to allow data from up to eight gauges to be recorded continuously and simultaneously. Strain gauges were modified so that they could be securely attached to ligaments using 4-0 braided nylon sutures. We tested the reliability of this fixation method by performing repeated measurements on each ligament. We used data only from strain gauges that exhibited no loosening or slipping during repeated testing. Each strain gauge was calibrated to read zero in the most lax position of the ligament. The dissected ankle preparations were secured to a Genucom Knee Analysis System (FARO Medical Technologies
tronics, Aloha, OR) 8
mm
in
length
were
Figure
1. Strain measured in the anterior talofibular
ligament.
198
.occurred between the neutral position and 20° of plantar flexion. The average total increase in strain through 50° of motion was 15%. Inversion and internal rotation moments increased ligament strain, whereas eversion and external rotation moments decreased strain in the ligament. This pattern occurred throughout the entire range of motion, to the greatest extent when the ankle was in plantar flexion. Strain in the calcaneofibular ligament (Fig. 2) progressively decreased as the ankle was moved from 20° of dorsiflexion to approximately 20° of plantar flexion. Strain increased slightly when the ankle was plantar flexed to 30°. Inversion or external rotation increased strain in the ligament, whereas eversion or internal rotation decreased strain in the ligament at all positions of dorsiflexion or plantar flexion. Strain in the long fibers of the posterior talofibular ligament (Fig. 3) increased when the ankle was moved into dorsiflexion or plantar flexion. Strain increased when the talus was externally rotated, but decreased when the talus was internally rotated in all positions except at 20° of dorsiflexion and 20° of plantar flexion. Strain in the posterior talofibular ligament decreased slightly when the talus was inverted, but increased slightly when it was everted. Strain in the anterior tibiofibular ligament (Fig. 4) increased 3% when the ankle was moved from the neutral position to 20° of dorsiflexion. Whereas strain was unaffected by inversion or eversion, external rotation of the talus increased strain and internal rotation of the talus decreased strain. This was true at all joint angles. The posterior tibiofibular ligament elongated up to a maximum of 3% as the ankle was moved from the neutral
Figure
2. Strain measured in the calcaneofibular
ligament.
Figure 3. Strain measured in the posterior talofibular ligament.
Figure 4. Strain measured in the anterior tibiofibular ligament.
199
Strain in the calcaneofibular ligament increased when the ankle was dorsiflexed. Strain also increased when inversion stress was applied to the ankle throughout the range of ankle motion, but especially with dorsiflexion. These findings are similar to those of Rasmussen.15 Strain in the calcaneofibular ligament did not increase when the talus was internally rotated; this differs from the findings of Leonard,l° and McCullough and Burge.’1 Our results support Rasmussen’s findings that the calcaneofibular ligament also prevents excessive external talar rotation. We measured relatively low strains of the calcaneofibular ligament during all tests, supporting Rasmussen’s conclusion that the calcaneofibular ligament does not play an independent role in ankle joint stability, but rather acts primarily as a guide for the axis of subtalar motion, as described by Inman.4 In clinical situations where the anterior talofibular ligament is ruptured, the calcaneofibular ligament may become the subsequent primary restraint to talar inversion. Our data support the concept that the anterior talofibular and calcaneofibular ligaments function together at all positions of ankle flexion to provide lateral ankle stability. The anterior talofibular ligament plays a primary role when the ankle is in plantar flexion, and the calcaneofibular ligament is an important stabilizing structure when the ankle is
Figure
5. Strain measured in the
posterior
tibiofibular
liga-
ment.
position to 20° of dorsiflexion (Fig. 5). Strain in the ligament decreased with external rotation and increased with internal rotation of the talus.
DISCUSSION Strains of greater than 5% were measured in some of the ankle ligaments. Our measurements do not reflect the true stress-strain properties of the ligaments themselves, but rather, are measures of apparent changes in ligament length within the range of motion tested. The strain patterns we found in the anterior talofibular ligament are similar to those found in other studies where investigators concluded that this ligament resists plantar flexion and internal rotation.7, 15, IS Contrary to one report, 15 we did not measure increased strain in the anterior talofibular ligament when the ankle was dorsiflexed. Our finding that strain in the anterior talofibular ligament increased with inversion at all ankle positions is consistent with the work of Johnson et al.,~who found that dividing the anterior talofibular ligament increased the talar tilt at all flexion angles. Our data contradict reports that the anterior talofibular ligament plays a minimal role in limiting inversion or that it resists inversion only in plantar flexion.&dquo; This study emphasizes the importance of the anterior talofibular ligament in limiting internal rotation and inversion, confirming our belief that it is the most important ligament to repair when performing surgical reconstruction for lateral ankle instability.
dorsiflexed. Strain in the posterior talofibular ligament increased when the talus was dorsiflexed, plantar flexed, and exter-
nally rotated. Inversion caused minimal change in strain. This finding supports the conclusion that the posterior talofibular ligament is not a significant structure in inversion-internal rotation ankle injuries.17 We did not measure strain in the short anterior fibers of the posterior talofibular ligament. However, Rasmussen15 showed that these fibers resist inversion stress. Extreme dorsiflexion and external rotation of the talus greatly increased strain in the posterior talofibular ligament. This finding is consistent with our clinical experience of frequently finding tenderness in the posterior talofibular area in patients who have sustained dorsiflexion-external rotation ankle injuries. Rasmussen was able to rupture the posterior talofibular ligament in cadaver ankles by applying dorsiflexion and external rotation stresses. Strain in the anterior tibiofibular ligament increased when the ankle was moved into extreme dorsiflexion and external rotation. This finding supports Kleiger’s study,’ in which he was able to disrupt the anterior tibiofibular ligament by dorsiflexing and externally rotating the ankle. Strain in the posterior tibiofibular ligament increased when the ankle was dorsiflexed but, unlike the anterior tibiofibular ligament, strain diminished when the ankle was externally rotated and increased when the talus was internally rotated. These findings support the concept that both the anterior and posterior tibiofibular ligaments can tear as a result of a dorsiflexion injury, but an external rotation injury that does not totally disrupt the tibiofibular syndesmosis should spare the posterior tibiofibular ligament. Posterolateral ankle tenderness following an external rotation injury is more likely
200
sign of a torn posterior talofibular ligament than posterior tibiofibular ligament. a
a
torn
REFERENCES 1 2
Anderson KJ, Lecocq JF Operative treatment of injury to the fibular collateral ligament of the ankle J Bone Joint Surg 36A 825-832, 1954 Arms S, Boyle J, Johnson R, et al Strain measurement in the medial collateral ligament of the human knee An autopsy study J Biomech 16
Injuries of the lateral ligaments of the ankle A clinical and experimental study J Bone Joint Surg 31A 373-377, 1949 11 McCullough CJ, Burge PD Rotatory stability of the load-bearing ankle An experimental study J Bone Joint Surg 62B 460-464, 1980 12 Monahan JJ, Gngg P, Pappas AM, et al In vivo strain patterns in the four major canine knee ligaments J Orthop Res 2 408-418, 1984 13 Parlasca R, Shoji H, D’Ambrosia RD Effects of ligamentous injury on ankle and subtalar joints A kinematic study Clin Orthop 140 266-272, 1979 10
Leonard MH
14 15
Pennal GF Subluxation of the ankle Can Med Assoc J 49 92-95, 1943 Rasmussen O Stability of the ankle joint Analysis of the function and traumatology of the ankle ligaments Acta Orthop Scand 56 (Suppl 211)
491-496,1983 3 Dias LS The lateral ankle sprain An
experimental study
J Trauma 19
266-269,1979 4 Inman VT The Joints of the Ankle Baltimore, Williams & Wilkins, 1976 5 Johnson EE, Markolf KL The contribution of the anterior talofibular ligament to ankle laxity J Bone Joint Surg 65A 81-88, 1983 6 Kennedy JC, Hawkins RJ, Willis RB Strain gauge analysis of knee ligaments Clin Orthop 129 225-229, 1977 7 Kleiger B The mechanism of ankle Injuries J Bone Joint Surg 38A 59-70, 1956 8 Laurin C, Mathieu J Sagittal mobility of the normal ankle Clin Orthop 108
99-104,1975 9 Launn CA, Quellet R, St Jacques R: Talar and subtalar tilt An experimental investigation Can J Surg 11 (3) 270-279, 1968
1-75, 1985 16 Rubin G, Witten M The talar-tilt angle and the fibular collateral ligaments A method for the determination of talar tilt J Bone Joint Surg 42A 311-
326,1960 Ruth CJ The surgical treatment of Injuries of the fibular collateral ligaments of the ankle J Bone Joint Surg 43A 229-239, 1961 18 Sammarco GJ, Burstein AH, Frankel VH Biomechanics of the ankle A kinematic study Orthop Clin North Am 4 75-96, 1973 19 Shybut GT, Hayes W, White AA III Normal patterns of ligament loading among the lateral collateral ligaments Trans Orthop Res Soc 8 15, 1983 20 Stormont DM, Morrey BF, An KN, et al Stability of the loaded ankle Relation between articular restraint and primary and secondary static restraints Am J Sports Med 13 295-300, 1985 17
ligaments MARK R.
COLVILLE,* MD, RICHARD A. MARDER, MD, JOHN J. BOYLE, MD, AND BERTRAM ZARINS, MD
From the
Orthopaedic Service, Massachusetts General Hospital, Boston, Massachusetts posterior tibiofibular ligament
ABSTRACT
tears with extreme dor-
siflexion. We measured strain in the lateral ligaments of 10 human cadaver ankles while moving the ankle joint and applying stress in a variety of ways. We studied the anterior talofibular, calcaneofibular, posterior talofibular, anterior tibiofibular, and posterior tibiofibular ligaments. Strain measurements in the ligaments were recorded continuously while the ankle was moved from dorsiflexion into plantar flexion. We then repeated measurements while applying inversion, eversion, internal rotation, and external rotation forces. Strain in the anterior talofibular ligament increased when the ankle was moved into greater degrees of plantar flexion, internal rotation, and inversion. Strain in the calcaneofibular ligament increased as the talus was dorsiflexed and inverted. These findings support the concept that the anterior talofibular and calcaneofibular ligaments function together at all positions of ankle flexion to provide lateral ankle stability. We measured maximum strain in the posterior talofibular ligament when the ankle was dorsiflexed and externally rotated. The strain in the anterior and posterior tibiofibular ligaments increased when the ankle was dorsiflexed. External rotation increased strain in the anterior tibiofibular ligament and decreased strain in the posterior tibiofibular ligament. Based upon strain measurements in the lateral ankle ligaments in various ankle joint positions, we believe the anterior talofibular ligament is most likely to tear if the ankle is inverted in plantar flexion and internally rotated. Theoretically, the calcaneofibular ligament tears primarily in inversion if the ankle is dorsiflexed; the anterior tibiofibular ligament tears in dorsiflexion, especially if combined with external rotation; and the
Ankle ligament sprains are common injuries. The roles that various ankle ligaments play in resisting excess forces remain unclear, however. Successful repair of torn ligaments and reconstruction of chronically unstable ankles require a clear understanding of the function of the ankle ligaments. Leonardl° and Anderson and LeCocq’ studied lateral ankle ligaments at surgery and during anatomical dissections. Several investigators have measured talar displacement and rotation after selective sectioning of various ligaments, but often with conflicting results.3, 5, 9, m> 13-15, Zo Others used radiographic techniques to measure changes in ankle stability after various injuries or experimentally induced ligament disruptions.8,16 The problem with ligament cutting studies is that ankle biomechanics are altered and the findings are not derived from measurements of dynamic relationships of the various ligaments. Shybut et a1.19 measured forces in intact ankle ligaments using buckle transducers. They found that there was little tension in lateral ankle ligaments through most of the range of normal ankle motion. Kennedy et al.,s Arms et al.,2 and Monahan et a1.12 used mercury-filled strain gauges to measure strain in intact knee ligaments. They measured strain without altering the ligament characteristics or joint mechanics. The purposes of this study were to measure strain in intact ankle ligaments during dorsiflexion and plantar flexion and to measure changes in strain when the ankle was inverted, everted, internally rotated, and externally rotated.
MATERIALS AND METHODS
Specimens *
Address correspondence and repnnt requests to: Mark R Colvdle, MD, Division of Orthopedics and Rehabilitation, The Oregon Health Sciences University, 3181 S W Sam Jackson Park Road, Portland, OR 97201.
Ten human ankles were tested. Three specimens were from fresh cadavers and seven had been frozen for less than 1 196
197
month. The average age of the specimens was 64 years, the range being 28 to 79 years. Most of the amputations had been performed because of ischemic vascular disease. The skin and soft tissues were removed and the ligaments and bones were left intact. If the specimen came from a below-knee amputation, the fibula was stabilized to the tibia using a screw placed as proximally as possible in order to minimize the effect of the screw on normal joint mechanisms. The screw held the fibula in its proper orientation to the tibia and maintained normal tension in the interosseous membrane. In above-knee amputation specimens, the knee was disarticulated and the proximal tibiofibular joint was left intact. The forefoot was transected through the metatarsal bones.
Mounting Three smooth Steinmann pins each 5 mm in diameter were drilled transversely through the tibia at a level approximately 15 cm above the ankle joint. The pins were secured to each other using modified Hoffman clamps. A 5 mm diameter pin was drilled into the anterior talus from an anterior to posterior direction passing through the space between the first and second metatarsal bones. This pin transfixed the first cuneiform and navicular bones and passed into the talus through its center of rotation. Two Schanz screws 6 mm in diameter were drilled across the subtalar joint passing through the calcaneus into the talus parallel to the longitudinal axis of the tibia. Subtalar joint motion was eliminated so that strain in the calcaneofibular ligament could be measured in relation to ankle joint motion only. The anterior screw passed through the center of rotation of the talus. This fixation eliminated motion at the subtalar joint.
Inc., Montreal, Canada). This computerized system enabled to measure displacements using an electrogoniometer and to measure forces that were applied using a force plate. The Genucom computer was also interfaced with the Apple IIC computer to allow simultaneous display of data, such as strain versus flexion angle and joint force. The anterior talofibular, calcaneofibular, and the long fibers of the posterior talofibular, anterior tibiofibular, and posterior tibiofibular ligaments were studied. After the strain gauges were attached to the ligaments, the ankles were moved through a full range of motion several times. The gauges were rechecked to be sure no slippage had us
occurred. The ankles
were
moved from 20° of dorsiflexion
plantar flexion while no versional or rotational forces were applied. Strain was measured continuously in each ligament through this range of motion. Strain was then measured continuously in each ligament through the range of motion while moments of 3 Nm of internal rotation, external rotation, inversion, and eversion were applied to
to 30° of
the talus.
Although a weightbearing model would have been preferable, the constraints of our testing apparatus did not allow us to apply a physiologic load across the ankle joint while measuring strain. RESULTS Strain in the anterior talofibular ligament (Fig. 1) progressively increased as the ankle was moved from 20° of dorsiflexion to 30° of plantar flexion. The greatest rate of increase
Instrumentation
Mercury-filled Silastic strain
gauges
(Parks Medical Elec-
used. The inner diameter of each was 0.30 mm and the outer diameter was 0.64 mm. The electrical resistance of the strain gauges, which changed as a function of length, was processed using an eight-channel metering system. This system produced a linear voltage output for strains between 0% and 20%. Calibration curves for each strain gauge were made at 100 jAm increments to confirm that each gauge had a linear output. The meter was interfaced with an Apple IIC computer to allow data from up to eight gauges to be recorded continuously and simultaneously. Strain gauges were modified so that they could be securely attached to ligaments using 4-0 braided nylon sutures. We tested the reliability of this fixation method by performing repeated measurements on each ligament. We used data only from strain gauges that exhibited no loosening or slipping during repeated testing. Each strain gauge was calibrated to read zero in the most lax position of the ligament. The dissected ankle preparations were secured to a Genucom Knee Analysis System (FARO Medical Technologies
tronics, Aloha, OR) 8
mm
in
length
were
Figure
1. Strain measured in the anterior talofibular
ligament.
198
.occurred between the neutral position and 20° of plantar flexion. The average total increase in strain through 50° of motion was 15%. Inversion and internal rotation moments increased ligament strain, whereas eversion and external rotation moments decreased strain in the ligament. This pattern occurred throughout the entire range of motion, to the greatest extent when the ankle was in plantar flexion. Strain in the calcaneofibular ligament (Fig. 2) progressively decreased as the ankle was moved from 20° of dorsiflexion to approximately 20° of plantar flexion. Strain increased slightly when the ankle was plantar flexed to 30°. Inversion or external rotation increased strain in the ligament, whereas eversion or internal rotation decreased strain in the ligament at all positions of dorsiflexion or plantar flexion. Strain in the long fibers of the posterior talofibular ligament (Fig. 3) increased when the ankle was moved into dorsiflexion or plantar flexion. Strain increased when the talus was externally rotated, but decreased when the talus was internally rotated in all positions except at 20° of dorsiflexion and 20° of plantar flexion. Strain in the posterior talofibular ligament decreased slightly when the talus was inverted, but increased slightly when it was everted. Strain in the anterior tibiofibular ligament (Fig. 4) increased 3% when the ankle was moved from the neutral position to 20° of dorsiflexion. Whereas strain was unaffected by inversion or eversion, external rotation of the talus increased strain and internal rotation of the talus decreased strain. This was true at all joint angles. The posterior tibiofibular ligament elongated up to a maximum of 3% as the ankle was moved from the neutral
Figure
2. Strain measured in the calcaneofibular
ligament.
Figure 3. Strain measured in the posterior talofibular ligament.
Figure 4. Strain measured in the anterior tibiofibular ligament.
199
Strain in the calcaneofibular ligament increased when the ankle was dorsiflexed. Strain also increased when inversion stress was applied to the ankle throughout the range of ankle motion, but especially with dorsiflexion. These findings are similar to those of Rasmussen.15 Strain in the calcaneofibular ligament did not increase when the talus was internally rotated; this differs from the findings of Leonard,l° and McCullough and Burge.’1 Our results support Rasmussen’s findings that the calcaneofibular ligament also prevents excessive external talar rotation. We measured relatively low strains of the calcaneofibular ligament during all tests, supporting Rasmussen’s conclusion that the calcaneofibular ligament does not play an independent role in ankle joint stability, but rather acts primarily as a guide for the axis of subtalar motion, as described by Inman.4 In clinical situations where the anterior talofibular ligament is ruptured, the calcaneofibular ligament may become the subsequent primary restraint to talar inversion. Our data support the concept that the anterior talofibular and calcaneofibular ligaments function together at all positions of ankle flexion to provide lateral ankle stability. The anterior talofibular ligament plays a primary role when the ankle is in plantar flexion, and the calcaneofibular ligament is an important stabilizing structure when the ankle is
Figure
5. Strain measured in the
posterior
tibiofibular
liga-
ment.
position to 20° of dorsiflexion (Fig. 5). Strain in the ligament decreased with external rotation and increased with internal rotation of the talus.
DISCUSSION Strains of greater than 5% were measured in some of the ankle ligaments. Our measurements do not reflect the true stress-strain properties of the ligaments themselves, but rather, are measures of apparent changes in ligament length within the range of motion tested. The strain patterns we found in the anterior talofibular ligament are similar to those found in other studies where investigators concluded that this ligament resists plantar flexion and internal rotation.7, 15, IS Contrary to one report, 15 we did not measure increased strain in the anterior talofibular ligament when the ankle was dorsiflexed. Our finding that strain in the anterior talofibular ligament increased with inversion at all ankle positions is consistent with the work of Johnson et al.,~who found that dividing the anterior talofibular ligament increased the talar tilt at all flexion angles. Our data contradict reports that the anterior talofibular ligament plays a minimal role in limiting inversion or that it resists inversion only in plantar flexion.&dquo; This study emphasizes the importance of the anterior talofibular ligament in limiting internal rotation and inversion, confirming our belief that it is the most important ligament to repair when performing surgical reconstruction for lateral ankle instability.
dorsiflexed. Strain in the posterior talofibular ligament increased when the talus was dorsiflexed, plantar flexed, and exter-
nally rotated. Inversion caused minimal change in strain. This finding supports the conclusion that the posterior talofibular ligament is not a significant structure in inversion-internal rotation ankle injuries.17 We did not measure strain in the short anterior fibers of the posterior talofibular ligament. However, Rasmussen15 showed that these fibers resist inversion stress. Extreme dorsiflexion and external rotation of the talus greatly increased strain in the posterior talofibular ligament. This finding is consistent with our clinical experience of frequently finding tenderness in the posterior talofibular area in patients who have sustained dorsiflexion-external rotation ankle injuries. Rasmussen was able to rupture the posterior talofibular ligament in cadaver ankles by applying dorsiflexion and external rotation stresses. Strain in the anterior tibiofibular ligament increased when the ankle was moved into extreme dorsiflexion and external rotation. This finding supports Kleiger’s study,’ in which he was able to disrupt the anterior tibiofibular ligament by dorsiflexing and externally rotating the ankle. Strain in the posterior tibiofibular ligament increased when the ankle was dorsiflexed but, unlike the anterior tibiofibular ligament, strain diminished when the ankle was externally rotated and increased when the talus was internally rotated. These findings support the concept that both the anterior and posterior tibiofibular ligaments can tear as a result of a dorsiflexion injury, but an external rotation injury that does not totally disrupt the tibiofibular syndesmosis should spare the posterior tibiofibular ligament. Posterolateral ankle tenderness following an external rotation injury is more likely
200
sign of a torn posterior talofibular ligament than posterior tibiofibular ligament. a
a
torn
REFERENCES 1 2
Anderson KJ, Lecocq JF Operative treatment of injury to the fibular collateral ligament of the ankle J Bone Joint Surg 36A 825-832, 1954 Arms S, Boyle J, Johnson R, et al Strain measurement in the medial collateral ligament of the human knee An autopsy study J Biomech 16
Injuries of the lateral ligaments of the ankle A clinical and experimental study J Bone Joint Surg 31A 373-377, 1949 11 McCullough CJ, Burge PD Rotatory stability of the load-bearing ankle An experimental study J Bone Joint Surg 62B 460-464, 1980 12 Monahan JJ, Gngg P, Pappas AM, et al In vivo strain patterns in the four major canine knee ligaments J Orthop Res 2 408-418, 1984 13 Parlasca R, Shoji H, D’Ambrosia RD Effects of ligamentous injury on ankle and subtalar joints A kinematic study Clin Orthop 140 266-272, 1979 10
Leonard MH
14 15
Pennal GF Subluxation of the ankle Can Med Assoc J 49 92-95, 1943 Rasmussen O Stability of the ankle joint Analysis of the function and traumatology of the ankle ligaments Acta Orthop Scand 56 (Suppl 211)
491-496,1983 3 Dias LS The lateral ankle sprain An
experimental study
J Trauma 19
266-269,1979 4 Inman VT The Joints of the Ankle Baltimore, Williams & Wilkins, 1976 5 Johnson EE, Markolf KL The contribution of the anterior talofibular ligament to ankle laxity J Bone Joint Surg 65A 81-88, 1983 6 Kennedy JC, Hawkins RJ, Willis RB Strain gauge analysis of knee ligaments Clin Orthop 129 225-229, 1977 7 Kleiger B The mechanism of ankle Injuries J Bone Joint Surg 38A 59-70, 1956 8 Laurin C, Mathieu J Sagittal mobility of the normal ankle Clin Orthop 108
99-104,1975 9 Launn CA, Quellet R, St Jacques R: Talar and subtalar tilt An experimental investigation Can J Surg 11 (3) 270-279, 1968
1-75, 1985 16 Rubin G, Witten M The talar-tilt angle and the fibular collateral ligaments A method for the determination of talar tilt J Bone Joint Surg 42A 311-
326,1960 Ruth CJ The surgical treatment of Injuries of the fibular collateral ligaments of the ankle J Bone Joint Surg 43A 229-239, 1961 18 Sammarco GJ, Burstein AH, Frankel VH Biomechanics of the ankle A kinematic study Orthop Clin North Am 4 75-96, 1973 19 Shybut GT, Hayes W, White AA III Normal patterns of ligament loading among the lateral collateral ligaments Trans Orthop Res Soc 8 15, 1983 20 Stormont DM, Morrey BF, An KN, et al Stability of the loaded ankle Relation between articular restraint and primary and secondary static restraints Am J Sports Med 13 295-300, 1985 17
