Biomechanical Examination Because private practitioners are currently unable to access the complex machinery necessary to perform research quality 3-dimensional gait evaluations, they are forced to rely upon specific static and dynamic measurements that theoretically predict triplanar motions present during the gait cycle. For almost a century, researchers have been attempting to refine these measurements. In the early 1900â€™s, Dudley Morton (1) developed a foot classification system based on the respective lengths of the individual metatarsals. His theory that a shortened first metatarsal could identify overpronators has since been disproved (2). In 1949, Hiss (3) published his text Functional Foot Disorders in which he incorporated a more complicated classification system where various morphological and dynamic relationships were assessed and related to altered function; e.g., hypermobility of the first ray was identified by evaluating intermetatarsal movement ratios and was believed to be associated with the development of forefoot pathology. Despite problems with reproducibility, many foot specialists continue to use this biomechanical approach today (4). In 1971, Root et al. (5) published what is without doubt the most widely referenced source on biomechanical measurements. In their text Biomechanical Examination of the Foot, they describe a range of specific goniometric biomechanical measurements that were theorized to predict 3-dimensional motion patterns present during the gait cycle. In turn, these measurements were used to justify specific aspects of orthotic intervention. Although Root et al. (5) were pioneers in the field of biomechanics, their described measurements were difficult to reproduce (6) and it was later proven that their off weight-bearing measurements did not reflect the true ranges available during weight-bearing (7). More importantly, the various goniometric measurements suggested by the authors did not predict 3-dimensional lower extremity motions present during the gait cycle (810). This was first noted in 1989 by Hamill et al. (9). Using a handheld goniometer, these researchers measured the 16 static and dynamic variables described by Root et al. and then evaluated 3-dimensional motion as 24 subjects walked over a force platform. Unfortunately, not one of the static measurements predicted dynamic motion. In a similar study, McPoil and Cornwall (8) took 17 static and dynamic measurements on 27 young adults and performed 2-dimensional analysis of rearfoot motion during walking. Again, none of the static measurements predicted dynamic motion.
The complete inability of static measurements to predict dynamic function has become a major obstacle in the development of a scientifically justified algorithm for managing gait disorders. To help resolve this issue, several investigators have developed and evaluated a range of biomechanical measurements to determine if any of these measurements correlate with dynamic function. The ideal biomechanical measurement, besides predicting motion, should be repeatable between different examiners (i.e., possess high interrater reliability) and provide information that justifies clinical intervention. This chapter reviews these measurements as they are performed during the standard biomechanical examination. Supine Examination This examination should begin by motion palpating the various lower extremity articulations. The presence of joint dysfunction should be noted, and the fixations should be gently mobilized. In addition to relaxing the patient, this helps to reduce any functional deformities that might adÂ versely affect measurements. A quick visual assessment of muscle symmetry should be performed and if asymmetry is noted, particularly in the VMO or calf, circumference measurements should be taken. Next, a simple screening of muscle flexibility can be performed by moving each of the lower extremity joints through specific ranges of motion (refer back to figures 4.113 through 4.129). Excessive tightness/laxity should be noted and side-to-side differences in flexibility should be recorded. Ligamentous integrity of the knee and ankle can be evaluated using the specific orthopedic tests illustrated in Fig. 5.1 through 5.5. It is especially important to check the integrity of the anterior talofibular ligament, since laxity in this ligament increases the transfer of calcaneal eversion into internal tibial rotation (11), potentially producing injury in the proximal structures. The relative lengths of the metatarsals can be determined by plantarflexing the digits and comparing the locations of the dorsal metatarsal heads (see Fig. 4.76). The presence of shortened/lengthened metatarsals should be noted. A standard goniometer is then used to measure the range of hallux dorsiflexion (Fig. 5.6). Although off weight-bearing measurement of first metatarsophalangeal joint dorsiflexion is not predictive of 3-dimensional motion during the gait cycle, it is useful for monitoring the progression of osteoarthritis and/or for evaluating the efficacy of manual techniques when attempting to 271
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Figure 5.1. Medial collateral ligament (MCL) is tested with the valgus stress test, in which the knee is flexed 30° and a valgus stress is applied at the knee (A). The lateral collateral ligament (LCL) is also performed with the knee flexed 30°, only a varus stress is applied at the knee (B).
Figure 5.2. The anterior cruciate ligament (ACL) is tested with the modified anterior drawer test (A). This test is performed with the patient’s foot grasped between the examiners knees. The ACL is tested with the knee flexed 30° and the examiner pulling the proximal tibia forward while simultaneously palpating the femoral condyles with the thumbs. The posterior cruciate ligament (PCL) is tested by flexing the patient’s knee to 90° and applying a posteriorly directed force. Laxity should be compared bilaterally.
Figure 5.3. Specialty tests. Because the diagnostic accuracy of the anterior drawer test is poor, the ACL may also be evaluated with Lachman’s test (A). To perform this test, the patient is positioned with the knee slightly flexed and the leg externally rotated 20° while the examiner stabilizes the distal femur with one hand while attempting to displace the proximal tibia anteriorly with the other hand (arrow). The hand on the proximal tibia is positioned with the thumb and index finger placed on the joint line. The integrity of the posterolateral ligament complex can be evaluated with the Dial Test (B). This test is performed by flexing the knee of the supine patient 30° with one hand palpating the joint line while the opposite hand attempts to externally rotate the leg (arrow). If laxity of the posterolateral ligament complex is present, the forefoot will abduct excessively. This test is also helpful for evaluating the anterior and posterior cruciate ligaments. To test the anterior cruciate ligament, the knee is flexed 90° and the examiner attempts to internally rotate the knee by adducting the forefoot. The posterior cruciate ligament is also tested with the knee flexed 90°, only now the dial test is performed by abducting the forefoot. By visually aligning the distal pole of the patella with the tibial tuberosity, the examiner can evaluate even subtle differences in laxity.
Chapter Five Biomechanical Examination
Figure 5.4. Possible tears in the menisci are evaluated with McMurrayâ€™s test. The medial meniscus is evaluated by extending the fully flexed knee while externally rotating the leg (A) as a valgus stress is applied at the knee (B). An audible clunk is indicative of a tear. The lateral meniscus is tested by internally rotating the leg while applying a varus stress at the knee.
Figure 5.5. The modified anterior drawer (A) and a varus stress test (B) evaluate the integrity of the anterior talofibular ligament (ATFL) and the calcaneofibular ligament, respectively. The anterior drawer test is performed by stabilizing the patientâ€™s dorsal foot with one hand, while the opposite hand displaces the tibia straight posteriorly (arrow in A). When an isolated tear of the ATFL is present (C), the leg externally rotates with the applied stress (curved arrow). If both the deltoid (D) and anterior talofibular ligaments are torn, the leg will displace straight posteriorly with no rotational component to the motion. To test the calcaneofibular ligament with the varus stress test, the examiner applies a varus stress at the talocrural joint while the opposite hand palpates the joint line for gapping. As with all stress tests, laxity should be compared bilaterally.
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Human Locomotion: The Conservative Management of Gait-Related Disorders testing strength in the hip extensors, check for excessive cocontraction of the erector spinae, because this may be a factor in chronic pain and should be addressed with exercises that isolate the gluteus maximus. In addition, a suspected limb length discrepancy should be evaluated and specific muscles should be checked for contrac ture and/or weakness; e.g., tightness in the iliopsoas and quadratus lumborum muscles are notorious for producing functionally shortened limbs. Seated Examination The seated examination is used primarily as a screen for patellar tracking. With the knees positioned just beyond the edge of the examination table, the patient is instructed to flex and extend the lower legs while the examiner palpates medial and lateral aspects of the patella. Ideally, the normal patella will move in a C-shaped pattern with approximately 3 mm medial and lateral displacement while the leg extends. Additionally, the lateral aspect of the patella should tilt upwardly approximately 5°-7° when the knee is flexed between 45° and 18°, and terminal extension should be associated with downward tilt of the lateral aspect of the patella when the patella moves beyond the lateral femoral condyle (refer back to figure 2.53 and 2.54). These slight frontal and transverse plane movements are normal and should not be misdiagnosed as faulty tracking. Because it predisposes to retropatellar injury, the point in which vastus medialis obliquus attaches to the patella should be evaluated: a high attachment point limits the mechanical advantage of the inner quadriceps muscle and should be treated with strengthening exercises (Fig. 5.17). The final portion of the seated examination should include palpating the central portions of the vastus medialis obliquus and vastus lateralis while the patient performs a maximal isometric contraction of the quadriceps muscle: tone differences between the two portions of the quadriceps provides important information regarding the individual’s ability to recruit these muscles (Fig. 5.18).
Figure 5.17. The most distal aspect of the vastus medialis obliquus muscle (VMO) normally attaches to a point along the medial aspect of the patella (A). Because a high attachment of the VMO (B) limits the ability of this muscle to resist lateral displacement of the patella, it should be treated with specific VMO and/or hip external rotator strengthening exercises to prevent abnormal tracking.
transverse plane motions (accounting for only 16 to 19% of the work performed), they were still clinically significant and therefore “deserve further investigation.” The most popular frontal plane measurement of the lower extremity is the calcaneal bisection. During static stance, an individual is classified as a pronator if the calcaneal bisection is everted more than 6° (48). Because static calcaneal eversion correlates poorly with triplanar motion during gait, Sell et al. (49) suggest evaluating the dynamic change in the calcaneal bisection line by noting the change in calcaneal alignment when the individual moves from the subtalar neutral position to a relaxed calcaneal stance position. Although these researchers confirm the interrater reliability is poor for the relaxed calcaneal stance position and fair for the neutral position, the reliability improved significantly when the difference between these two lines was measured. The authors state that although static measurements alone are relatively inaccurate, the actual measured degree of movement is much more reliable.
Standing Examination Early research into lower extremity biomechanics focused almost exclusively on frontal plane alignment of the heel. Until recently, it was assumed that alignment of the calcaneus would predict triplanar motion throughout the lower extremity; e.g., excessive eversion of the calcaneus during static stance would predict excessive pronation during the gait cycle. Unfortunately, 3-dimensional analysis confirms there is little correlation between frontal plane alignment of the calcaneus and 3-dimensional motions present when walking (46). This has caused some researchers to suggest that frontal plane measurements of the rearfoot be abandoned. In support of these measurements, McClay and Manal (47) analyzed triplanar motions during gait and concluded that although frontal plane motions were not as important as sagittal and 280
Chapter Five Biomechanical Examination kinematics variables in a group of life-long noninjured runners and compared this data to a matched control group of previously injured runners. Their results revealed the injury-free group had greater hamstring flexibility, more rapid initial pronation and greater supination of the rearfoot at initial heel contact; i.e., they made initial ground contact with the rearfoot inverted. In a recent and extremely well-designed study, Willems et al. (58) evaluated 3-dimensional kinematics and plantar pressures of 400 physical education students before they began their first year of university. The students were followed weekly and injury rates were evaluated as students completed a wide range of extramural activities. At the end of the year, 46 of 400 subjects developed exercise related lower leg pain with an increased incidence in women. Three-dimensional kinematic analysis revealed the injured group made initial ground contact with the medial and lateral heel areas making contact at the same time, whereas the uninjured group made ground contact by striking on the lateral side of the heel and quickly rolling to the medial heel area. This is consistent with the findings of Hreljac (57) in that noninjured individuals tend to make heel strike in a supinated position. Willems et al. (58) theorized that having heel strike occur on the supinated side of neutral may allow for more rapid pronation and better shock absorption. Given that 3-dimensional studies reveal that the foot does move into a neutral position during stance phase, that measurements taken in a neutral position have acceptable rates of intra and interrater reliability, and the clinical observation that an inverted heel strike is associated with noninjury, it makes sense that neutral position measurements be included in the biomechanical examination. This is consistent with research by Houck et al. (59), who demonstrate that in addition to being highly repeatable, the subtalar neutral position provides a common reference point necessary to differentiate foot function in subjects with pathology. Using an Optotrak 3-dimensional motion analyzer, these authors confirm that incorporating subtalar neutral as a starting reference point improves the ability to distinguish kinematic patterns while walking. Specifically, they identified an increased range of calcaneal eversion during early stance and greater first metatarsophalangeal joint dorsiflexion during late stance when using subtalar neutral as a reference point. One of the only problems with this measurement is that the term subtalar joint neutral position is inappropriate, since it is the talonavicular joint that is being placed into a neutral position. The belief that the subtalar joint can be placed in a neutral position has recently been questioned, because congruency between the talus and calcaneus can only be determined with various imaging techniques (60). Furthermore, no clear definition exists regarding the location of a neutral subtalar joint as some authors relate subtalar neutrality to a vertical calcaneus (61), while others
Figure 5.18. Palpation of the vastus medialis obliquus (VMO) and the vastus lateralis (VL) during maximal isometric contraction of the quadriceps. Normally, these two muscles contract at the same time with equal force. If the quality of the VMO contraction is poor or there is a delay in activation, the patient is instructed to palpate the muscle while performing isometric exercises and focus on preferentially isolating the VMO.
Despite the acceptable levels of both intra and interrater reliability for measurements taken in the neutral subtalar position (50-52), some authorities feel that because the foot does not move into a subtalar neutral position during the gait cycle, measurements using the neutral position as a reference should not be included in a biomechanical exam (53,54). Unfortunately, the research questioning the use of neutral position measurements was performed using 2-dimensional imaging, which is of limited value for predicting triplanar motion because it is unable to evaluate motion during the propulsive period. More recent 3-dimensional research repeatedly reveals that the foot does in fact move into the neutral position both at heel strike and again during propulsion (55,56). Clinical evidence that the subtalar joint should be in a neutral position prior to heel strike was demonstrated in an interesting study by Hreljac et al. (57). Unlike prior studies that evaluated injured individuals to see what made them different, these researchers evaluated kinetic and 281
Human Locomotion: The Conservative Management of Gait-Related Disorders claim that it occurs at various points throughout the joint’s range of motion. For example, Inman et al. (62) claim it occurs at that midway mark while Root et al. (5) claim it occurs one third of the distance from a fully everted position. To add to the confusion, Pearce (63) compared subtalar motion as determined from CT scans to external ranges of motion measured with a goniometer and noted that goniometric measurements overestimated subtalar motion by approximately threefold: subtalar motion measured by CT ranged from 5° to 16° while goniometric ranges of subtalar motion ranged from 39° to 54°. Because of confusion with defining subtalar neutral and because it is the talonavicular joint that is being placed in a congruent position, not the subtalar, Menz (64) suggests that the phrase “subtalar neutral position” be replaced with “talonavicular neutral position.” To support this statement, he references a small study by Officer et al. (65), who determined with X-rays that when subjects are placed in a talonavicular position, the head of the talus had maximal articular contact in the navicular acetabulum in both the transverse and sagittal planes and that this congruence diminished as the foot moved towards the end ranges of motion. As a result, it is suggested the term “subtalar neutral” be abandoned in favor of the more anatomically precise phrase of “talonavicular neutral.” The last frontal plane measurement to be discussed is the rearfoot-to-leg angle. This measurement involves measuring the angle formed between the calcaneal and tibial bisection lines (which were marked during the prone examination) while the individual stands in either doublelimb relaxed calcaneal stance or single-limb stance (Fig. 5.19). McPoil and Cornwall (66) demonstrate that the angle measured during single-limb stance represents the position the rearfoot/lower leg will assume during the midstance period of the gait cycle and serves as a clinical indicator of the degree of maximum rearfoot eversion present during the walking cycle. Tsai et al. (67) categorized feet as pronated if the rearfoot-to-leg angle during double-limb support was greater than 9°, neutral with 3°-9° and supinated with less than a 3° angle. The intrarater reliability for this measurement was good and the interrater reliability was excellent. Unfortunately, because the authors did not report whether bisection lines were erased before each examiner performed the measurement, the high interrater reliability reported in this study should be viewed cautiously, because it is especially difficult for different examiners to bisect the lower leg in a reliable manner. An alternate method to evaluate the rearfoot-toleg angle is to note the change in this angle when the individual moves from talonavicular neutral to single-limb stance. Although no studies have been done comparing the two techniques, the results of the study by Sell et al. (49) suggest that measuring the change in alignment between talonavicular neutral and single-limb stance may be more accurate than a single static measurement,
Figure 5.19. The standing rearfoot to leg angle. This measurement reproduces the angle formed between an 8 cm section of the lower leg and a 3 cm section of the bisected calcaneus. Drawn from a photograph in Tsai et al. (67).
because it measures the actual motion present as opposed to measuring possible errors with skin marks. To simplify this measurement, the talonavicular neutral angle may be measured off weight-bearing. Since the greatest amount of work performed during the gait cycle occurs in the sagittal plane (47), it is essential that the degree of ankle dorsiflexion be accurately evaluated. Because off weight-bearing measurements do not predict the range of motion available during the gait cycle, and because it is difficult to quantify the amount of force used while taking these measurements, several researchers have suggested that ankle dorsiflexion be measured only during full weight-bearing (68-70). In their study of fluid filled goniometers, Denegar et al. (68) performed weight-bearing ankle dorsiflexion measurements with the goniometers strapped to the subjects’ lower legs while they performed straight and bent knee lunges. The degree of weightbearing dorsiflexion was determined by measuring the lower leg angle present just before the plantar heel left the ground. The intrarater reliability for these measurements was excellent for the straight and bent knee measurements. The off weight-bearing and weight-bearing measurements of ankle dorsiflexion were significantly different in that the off weight-bearing straight knee measurements averaged 15.2°, while the weight-bearing straight knee measurements averaged 22.8°. An alternative to the fluid filled goniometer is to place a standard electric goniometer on the subject’s lower 282
Chapter Five Biomechanical Examination
Figure 5.20. The degree of weight-bearing ankle dorsiflexion is measured with the knee straight and bent with an electronic goniometer placed over the anterior aspect of the tibia.
leg during static stance and press the “zero” button. The subject is then asked to perform straight and bent knee lunges. Recordings are made of the angle of the lower leg as the heel is about to leave the ground (Fig. 5.20). Another simple method for evaluating weight-bearing ankle dorsiflexion is described by Vinicombe et al. (70). These authors suggest having a subject stand facing a wall while performing knee bends from different distances. The subject repositions the foot until anterior aspect of the knee touches the wall just as the heel is leaving the ground. The angle of the central tibia is then recorded. This technique is extremely useful for evaluating progress when attempting to restore ankle dorsiflexion using manual techniques. A controversial sagittal plane measurement of the first metatarsophalangeal joint is referred to as the Hubscher maneuver or Jack’s test. Initially described by Jack in 1954 (71), this test is used to identify functional hallux limitus (Fig. 5.21). Although individuals presenting with a positive Jack’s test were theorized to present with a wide range of compensatory movement patterns (e.g., an apropulsive gait, premature hip flexion and even forward head posture), the accuracy of this test to predict motions present during the gait cycle is questionable. In 2006, Halstead and Redmond (72) compared 15 individuals presenting with functional hallux limitus (as determined with Jack’s test) with an age and gender matched control group. After performing 3-dimensional motion analysis, the authors concluded there was no significant relationship between static and dynamic first metatarsophalangeal joint motion during the gait cycle since both groups dorsiflexed 36° during propulsion. This is not to suggest that this test should be abandoned. Even though both groups moved through similar ranges of motion, it is possible that there was greater articular compression in the dorsal aspect
of the first metatarsophalangeal joint in individuals presenting with a positive Jack’s test. Supporting this theory, Welsh et al. (131) evaluated hallux dorsiflexion in subjects with mechanical first metatarsophalangeal joint pain who were asked to walk with and without modified, prefabricated orthotics for 24 weeks. Although the orthotics had no effect on the range of propulsive period first metatarsophalangeal joint dorsiflexion (as measured with an electromagnetic tracking system), subjects wearing the orthotics reported significant reductions in pain by the end of the study. While the exact mechanism remains unclear, it is possible the orthotics altered pressure in the dorsal first metatarsophalangeal joint without altering motion.
Figure 5.21. The Hubscher maneuver or Jack’s test. Due to the windlass mechanism of the plantar fascia, dorsiflexion of the hallux during double-limb support is associated with a concomitant increase in arch height (A). This test is positive when hallux dorsiflexion comes to a halt with no sign of arch elevation (B).
Human Locomotion: The Conservative Management of Gait-Related Disorders In support of the arch index, McCrory et al. (80) demonstrates that it was highly correlated with navicular height while Kanatli et al. (81) demonstrates that the arch index is significantly related to angular measurements determined from radiographs. Although this information conflicts with the study by Hawes et al. (78) showing no connection between footprints and arch shape, the research by Hawes et al. (78) was flawed because they used a caliper method to identify arch structure, which is inappropriate since variations in the thickness of the soft tissues beneath the arch may mask true arch shape (82). More recent research by Menz and Muntana (83) confirms the arch index is highly correlated with arch height, suggesting this measurement may be useful when performing a biomechanical exam. Despite the correlation between the arch index and arch height, a major shortcoming of this technique is that the evaluation of footprints is significantly affected by body mass. In their article, The arch index: are we measuring fat or flat feet, Wearing et al. (84) conclusively demonstrate that the weight of an individual significantly distorts the resultant footprint. Because footprint parameters are so readily distorted by elevated body mass, they should be used only on non-obese individuals. Rather than attempting to identify shape of the longitudinal arch by looking at the plantar surface, Feiss (85) developed a more direct method of determining arch height by comparing the height of the navicular tuberosity relative to a line bisecting the medial malleolus and first metatarsal head. An arch was classified as high, medium or low depending on where the navicular tuberosity was relative to the bisection line (Fig. 5.23). Because this measurement supplies limited information about the exact degree of arch elevation, Dahle et al. (86) modified this concept by creating an angle system referred to as the
Perhaps the single most important component of a biomechanical exam is the ability to precisely quantify the height of the medial longitudinal arch. Because arch height predicts injury patterns and 3-dimensional motions present during the gait cycle (73,74), it is critical that the height of the medial longitudinal arch be accurately measured. One of the earliest methods for quantifying arch height focused on various indices associated with footprints. Popularized in 1947 by Harris and Beath (75), footprints obtained with an ink pedograph were thought to predict arch shape and allow for classification of low, medium, and high-arched feet. Cavanagh and Rodgers (76) refined various aspects of footprint evaluation and defined the arch index as the ratio of the area of the middle third of a footprint relative to the total area excluding the toes (Fig. 5.22). Early research on the arch index and footprints in general suggested that these measurements, although reliable, were poorly correlated with radiographic measurements of arch height (77). Hawes et al. (78) compared a wide range of footprint measurements (including the arch index) with a clinical measurement of arch height (using a digital caliper) and could find no correlation between any of the footprint parameters and the clinically measured arch height. This is consistent with Saltzman et al. (79) who stated that attempting to determine arch height by footprint analysis is comparable to attempting to determine the height of a building by measuring its width. To make matters worse, Hamill et al. (9) found that the arch index footprint measurement correlated poorly with rearfoot motion during barefoot walking while Kernozek and Ricard (79) found that the arch index was not predictive of eversion during shod running.
Figure 5.23. Feissâ€™ line. A line is drawn between the inferior aspect of the medial malleolus and the distal first metatarsal. A vertical line is then dropped directly through the navicular tuberosity (dotted line) and is divided into equal thirds. A cavus foot is present when the navicular tuberosity is situated near the upper border of the first division, while a pronated foot will often present with the navicular tuberosity in the second division.
Figure 5.22. The Arch Index. Although there are different formulas for calculating arch height based on footprints, Cavanagh and Rodgers (76) define the arch index as area B divided by the combined areas of A, B, and C.
Chapter Five Biomechanical Examination problem with the longitudinal arch angle is that it requires making several skin marks, which significantly increases the potential for measurement error. Because skin marks move during dynamic examination, accurate interpretation of movement during the gait cycle is difficult. To avoid having to use unreliable skin marks, Williams and McClay (82) developed an extremely useful measurement called the arch height ratio. Because palpation of the navicular tuberosity is difficult and because absolute height of the navicular may not be reflective of true arch height, these authors suggest that arch height is best measured by noting height of the dorsum of the foot at 50% foot length, and creating a ratio between height measured at that point and truncated foot length (i.e., the measured distance from the posterior heel to the center of the first metatarsophalangeal joint) (Fig. 5.25). Individuals with high arches have an arch height ratio greater than .356 and individuals with low arches have an arch height ratio less than .275. Creating a ratio is essential because any biomechanical measurement that does not take into account foot size is flawed; e.g., a man with a size 13 foot would present with different measurements than a child. This ratio is easy to measure and is extremely reliable, even when measured during different degrees of weight-bearing. To evaluate its ability to predict motion during the gait cycle, Franettovich et al. (91) performed a 2-dimensional study showing that the arch height ratio taken during double-limb static stance (i.e., 50% weightbearing) accurately predicted arch height present during the midstance period of walking and running. The authors state that because the static arch ratio requires making only one mark on the skin, it is more reliable than the longitudinal arch angle in determining dynamic foot position and it is “the simplest and most efficient measure to obtain” with the authors reporting excellent inter and intrarater reliability when measured during double-limb support. While the arch height ratio is an exceptional predictor of arch shape, it provides limited information concerning flexibility of the foot. In an attempt to categorize foot types by motion, Brody (92) developed the navicular drop test. This measurement involves marking the navicular tuberosity with a pen and measuring the height change when the subject moves from talonavicular neutral to double-limb relaxed stance. Alternate methods of measuring the navicular drop have been described in which the initial height of the navicular is measured either with the subject seated in talonavicular neutral (93) or just seated with the foot flat on the ground (48). Bennett et al. (94) suggest measuring navicular drop by noting the difference in navicular height when the standing subject shifts to single-limb stance. Because the different techniques often produce larger ranges of navicular drop measurements than the standard talonavicular neutral to double-limb support, they should be used with caution, since the numbers may not be interchangeable.
Figure 5.24. The Longitudinal Arch Angle. Excessive pronators often present with angles less than 130°, while supinators present with angles exceeding 150°. Drawn from a photograph in McPoil and Cornwall (87).
longitudinal arch angle. This measurement is performed by determining the obtuse angle formed by one line passing from the midpoint of the medial malleolus through the navicular tuberosity, and another line from the midpoint of the medial aspect of the first metatarsal head and the navicular (Fig. 5.24). Compared with Feiss’ line, this measurement provides more exact information about the degree of arch elevation. Although different researchers give different ranges for identifying pronators and supinators, a recent study by McPoil and Cornwall (87) suggests that pronators possess angles less than 130°, neutral arches have an angle between 130° and 150°, and supinators have angles greater than 150°. Although Jonson and Gross (88) found acceptable levels for inter and intrarater reliability when measuring the longitudinal arch angle, they failed to report whether their examiners erased skin marks before subsequent measurements, making their conclusions regarding interrater reliability of questionable value. In a larger and more detailed study, McPoil and Cornwall (87) did erase bisection lines and found interrater reliability to be significantly lower but still acceptable. In addition to determining reliability, these researchers also evaluated whether the longitudinal arch angle could predict dynamic foot posture. Using 2-dimensional analysis, McPoil and Cornwall (87) conclude that the longitudinal arch angle measured during static stance is highly predictive of foot posture present during the midstance period while walking. The authors repeated the study by evaluating the longitudinal arch angle in runners and found that the longitudinal arch angle was highly predictive of dynamic posture during stance phase of running, explaining more than 85% of motions present during midstance (89). This is consistent with the clinical observation that individuals with low longitudinal arch angles are more likely to develop medial tibial stress syndromes (90). Despite the acceptable interrater reliability, a major 285
Human Locomotion: The Conservative Management of Gait-Related Disorders
Figure 5.25. The Arch Height Ratio. This measurement is performed by noting the length of the foot at the distal aspect of the hallux (A). This number is divided by two and the height of the dorsal foot is measured at this point (B). The arch height ratio is determined by dividing the height of the dorsal foot by the length of the foot measured at the center of the first metatarsophalangeal joint (C). If the resultant number is less than .275, the arch is characterized as low, while people with high arches present with an arch height ratio greater than .356.
The significance of vertical displacement of the navicular was demonstrated by Mueller et al. (95), who used a 3-dimensional digitizer to evaluate movement of the navicular in 3 planes of motion and found that movement was the greatest in the sagittal plane (navicular drop), moderate in the transverse plane (navicular drift) and insignificant in the frontal plane. This is consistent with research by McClay and Manal (47), confirming the greatest amount of work performed during the gait cycle occurs in the sagittal plane. Because different techniques are used to measure navicular drop, typical ranges for the mean degree of navicular drop vary in the literature from a low of 3.6 mm reported by Bennett et al. (94) to a high of 10 mm reported by Brody (92). Loudon (125) suggests that individuals be categorized as supinators if the navicular drop is less than 6 mm, neutral with 6-9 mm, and pronators if they possess more than 9 mm of navicular drop. These numbers should be used cautiously as Loudonâ€™s (96) sample consisted of all females so the resultant numbers might be too low to be used on males with large feet (remember foot size can influence navicular drop since a size 14 foot would be expected to possess a larger degree of navicular drop than a size 6 foot). In one of the only studies reporting differences in navicular drop between males and females, Trimble et al. (97) evaluated 43 college students and found a mean navicular drop of 7.5 mm for males and 7.1 mm for females, suggesting that moderate differences between foot sizes may not be that significant. When performed by experienced practitioners, both intra and interrater reliability is acceptable (49,98). In a frequently referenced paper, Sell et al. (49) used
relatively inexperienced examiners (i.e., less than 4 hours of training using navicular drop measurement) and found their measurements possessed fair intra and good interrater reliability. Piciano (98) compared the ability of experienced and inexperienced practitioners to agree upon the measured degree of navicular drop and found the reliability was higher for the experienced practitioners. Because it is occasionally difficult to palpate the navicular tuberosity, an alternate method is to mark a spot on the dorsum of the foot at 50% foot length and measure the drop from talonavicular neutral to double-limb support. Although this technique has not been studied, it provides similar numbers to the navicular drop and would most likely produce a higher interrater reliability because marking the dorsum of the foot is more reliable than marking the navicular (which can be difficult in obese patients). To get around the problem of foot size affecting measurements, Barton et al. (99) suggest the navicular drop measurement be â€œnormalizedâ€? by dividing the measured degree of drop by the length of the foot (as measured from the posterior aspect of the calcaneus to the most distal point of the first or second toe, whichever is longest). Using this technique, these authors determined that navicular drop measured from talonavicular neutral to relaxed calcaneal stance in a pain-free population has good to excellent interrater reliability in experienced and inexperienced practitioners. To study the connection between navicular drop and kinematics during the gait cycle, McPoil and Cornwall (8) performed 2-dimensional video analysis of 27 healthy subjects and found that of the 17 measurements evaluated, only the navicular drop was able to predict maximum 286
Chapter Five Biomechanical Examination rearfoot pronation (although even this connection was weak, since it explained only 17% of the variance). More conclusive evidence exists concerning the connection between navicular drop and injury. Bennett et al. (94) demonstrate that the navicular drop predicts medial tibial stress syndromes with 76% accuracy, while DeLacerda (100) demonstrates that excessive navicular drop predicts anterior compartment pain in athletes. The connection between navicular drop and anterior cruciate ligament injury is also significant as Beckett et al. (101) compared navicular drop in 50 subjects with and 50 subjects without ACL rupture and noted the ACL injured group had significantly higher navicular drops (noninjured 6.9 mm, injured 13 mm). The relationship between excessive navicular drop and ACL injury has been studied by several different researchers and while one study found no connection (102), other studies have found a strong connection between ACL rupture and increased navicular drop (101,96). More recently, Allen and Glasoe (103) used a digital metricom system to compare navicular drop in subjects with a history of ACL rupture with age and sex matched controls. Again, there was a strong correlation between navicular drop and ACL injury as the injured group had a mean navicular drop of 10.5 mm compared to 8.1 mm in the uninjured group. To determine if there is a correlation between ACL laxity and navicular drop, Trimble et al. (97) performed an interesting study in which they evaluated the degree of genu recurvatum, the thigh foot angle, and the degree of navicular drop, and compared this information to the degree of laxity present in the ACL as determined by measuring tibial translation with a KT 1000 arthrometer. Although excessive genu recurvatum and an elevated thigh foot angle were not predictive of increased tibial translation, the navicular drop was. Because the connection between excessive navicular drop and ACL injury is so strong, it is logical to assume that a biomechanical explanation exists in which excessive navicular drop increases internal tibial rotation, which in turn increases subsequent valgus collapse at the knee (a proven predictor of ACL rupture). Although logical, this simple biomechanical model may not fully explain the actual mechanism because recent research by Joseph et al. (104) reveals an inverse relationship between the degree of navicular drop and maximum knee valgus following a jump from a 31 cm platform; i.e., the athletes with the highest degree of navicular drop had the straightest knees during the drop test. The authors attributed the straight knees to an “unrecognized protective mechanism” provided by the excessively pronated feet in which excessive pronation absorbed ground-reactive forces without altering lower extremity rotation. It is possible that rather than causing ACL injuries by producing excessive internal tibial rotation during contact, an excessive degree of navicular drop is simply a by-product of generalized ligamentous laxity,
a proven risk factor for the development of ACL rupture (105). Because the navicular drop only measures the sagittal plane component of navicular displacement and because the navicular has been shown to move a significant amount in the transverse plane (106), Menz (4) suggests using the navicular drift test. This measurement is performed by placing the standing subject in talonavicular neutral and measuring the number of millimeters the navicular moves in the transverse plane when the subject shifts from neutral to relaxed calcaneal stance (Fig. 5.26). An alternate technique is to measure the amount of movement as the patient shifts to single-limb stance (107). According to Menz (4), evaluation of both navicular drop and drift are easy to perform and provide more accurate information concerning the talonavicular joint than conventional frontal plane rearfoot measurements. As it is a relatively new test, there is little published information describing normal ranges and/or a correlation to dynamic function. In one of the first studies of intra and interrater reliability, Vinicombe et al. (107) evaluated the navicular drift measurement when subjects moved from talonavicular neutral to single-limb stance and noted relatively low rates of interrater reliability. The authors suggest that the poor results might have resulted from using the single-limb stance endpoint for measuring motion. They claim that because the height of the navicular in talonavicular neutral was reliable (which has been confirmed in other studies [6,50]), the poor outcomes were most likely the result of navicular movement that occurred during single-limb stance as “the subjects intermittently altered their standing to maintain balance.” Performing navicular drift from talonavicular neutral to relaxed double-limb calcaneal stance significantly improves reliability. As demonstrated by Barton et al. (99), measuring the degree of navicular drift when subjects move from talonavicular neutral to relaxed double-limb support is associated with high levels of interrater reliability, even when performed by inexperienced practitioners. A potential shortcoming of this measurement is that navicular drift, as with footprints, can be affected by body mass because obesity significantly distorts the measurement when the soft tissues beneath the arch bulge outwardly during weightbearing. Furthermore, individuals with hypertrophy of the abductor hallucis muscle (which is common in excessively pronated feet) are prone to mismeasurement because this muscle displaces the measuring device medially, resulting in a falsely elevated reading. To get around this problem, rather than measuring medial drift of the navicular, an alternate technique is to measure medial drift of the medial malleolus (109). The advantage of this technique is that skin marks are not necessary and obesity and muscle hypertrophy rarely affect the shape of the medial malleolus. This test is performed by placing the measuring device directly against the medial malleolus and noting the degree of medial drift when the 287
Human Locomotion: The Conservative Management of Gait-Related Disorders
Figure 5.26 The Navicular Drift Test. With the patient placed in a talonavicular neutral position (A), the horizontal component of the measuring device is placed on zero and positioned next to the navicular tuberosity (B). The top of the measuring device is now moved to the side and the patient is instructed to relax (C), allowing the navicular to move medially. The top of the measuring device is then moved back so it touches the navicular tuberosity and the degree in millimeters that the navicular tuberosity moved from the neutral to the resting position is then measured (D). Note that the lower portion of the device remains immobile throughout the measuring procedure.
Figure 5.27. The Medial Drift of the Medial Malleolus Test. As with medial drift of the navicular, this measurement is performed by placing the measuring device next to the medial malleolus with the talonavicular joint maintained in a neutral position (A). Once the top of the device is moved to the side, the patient is instructed to relax (B) and the top of the device is pushed back against the medial malleolus (C). The change in the horizontal position of the medial malleolus as the subject moves from talonavicular neutral to relaxed calcaneal stance is recorded. Because the patient may alter position of the medial malleolus by looking down during the procedure, the measurement is performed after instructing the patient to look forward and not down. Note that the same measuring device used to measure navicular drift is used to measure malleolar drift, only the top of the device is flipped horizontally so it can reach the malleolus.
Chapter Five Biomechanical Examination subject moves from talonavicular neutral into doublelimb stance (Fig. 5.27). Ranges for this measurement are similar to those found with medial drift of the navicular except they are smaller in obese patients. An individual is classified as a supinator with less than 5 mm medial drift, neutral with 5 to 10 mm, and a pronator with greater than 10 mm of medial drift of the medial malleolus. The total ranges available vary from 2 mm in rigid cavovarus foot types to 28 mm in extreme hyperpronators. By evaluating displacement of the medial malleolus, the examiner obtains important information regarding frontal plane motion of not just the rear and midfoot, but also the ankle. Although typically perceived as a pure hinge joint, in vivo analysis by Arndt et al. (110) confirms the talocrural joint everts more than 12Â° during stance phase. Measuring drift of the medial malleolus provides clinically useful information regarding frontal plane motions of this important joint. Furthermore, measuring medial drift of the medial malleolus allows for precise evaluation of the almost parallel translation occurring between the talus and calcaneus when the subtalar joint pronates. As described by Lundberg et al. (111), in vivo analysis of foot/ankle motion using surgically implanted tantalum beads reveals that pronation of the subtalar joint causes the talus to shift medially with a â€œsideward rolling action,â€? resulting in an almost parallel translation of the talus upon the calcaneus (Fig. 5.28). Measuring medial drift of the malleolus allows the practitioner to quantify the parallel translation, which provides information regarding the length of the lever arm body weight has for maintaining the foot in a pronated
Figure 5.29. As the talonavicular joint moves from a neutral to a pronated position, the lever arm afforded body weight for keeping the foot in a pronated position increases (compare X and Y).
position (Fig. 5.29). The larger lever arm afforded body weight requires the medial muscles generate more force to supinate the foot, possibly explaining why individuals who pronate excessively are more likely to present with injuries to their medial muscles and tendons (73). Medial drift of the medial malleolus measurement is similar to a more involved measurement known as the Ankle Valgus Index. Developed by Song et al. (114) this measurement allows the examiner to assess lengths of superimposed lever arms affecting the foot/ankle by creating a ratio between the center of the malleoli and the center of the foot (Fig. 5.30). Several studies confirm
Figure 5.30. The Ankle Valgus Index. Using a specially designed jig to superimpose the bisection of the malleoli over the foot, this measurement provides detailed information regarding the effective lengths of lever arms affecting the foot and ankle. Valgus Index equals (LA-LF) divided by LM, x100 where LA = distance between lateral malleolus (L) and malleoli bisection (A); LF = distance between lateral malleolus and foot bisection (F); LM = distance between lateral malleolus in medial malleolus (M). Drawn from Menz et al. (4).
Figure 5.28. As demonstrated by Lundberg et al. (111), pronation of the subtalar joint causes the talus to move with a medial rolling action upon the calcaneus.