Clinical Biomechanics PDF

Chapter 8 Introduction to clinical biomechanics with CHRISTIAN BARTON, NATALIE COLLINS and KAY CROSSLEY Mo Farah has nine key elements co his running technique that have allowed him co become Britain's greatest ever runner....

Chapter 8 Introduction to clinical biomechanics with CHRISTIAN BARTON, NATALIE COLLINS and KAY CROSSLEY Mo Farah has nine key elements co his running technique that have allowed him co become Britain's greatest ever runner. www.telegraph.co.uk, 16 September 2013 The term 'biomechanics' can be used in a variety of ways. Ultimately, biomechanical evaluation should be completed In this book, biomechanics refers to the description, analysis based on task specificity to ensure the clinician is confident and assessment of human movement during sporting in the accuracy of information obtained. activities. 1 Broadly, biomechanics can be broken into three categories, including 'kinematics' (movement we can see), 'IDEAL' LOWER LIMB 'kinetics' (forces driving the movement) and 'neuromotor' BIOMECHANICS-THE BASICS (muscle function controlling forces and movement). This Here we discuss ideal structural characteristics, including chapter will focus primarily on the actual movement available joint range of motion and stance position. Note occurring in the body segments (kinematics). Our approach that each individual has his or her own mechanical make-up can be referred to as 'subjective biomechanical analysis'. We due to structural characteristics (anatomy), and may never aim to describe movement such as running or squatting as achieve the 'ideal' position or biomechanical function. it appears to visual observation. This reflects how clinicians Table 8.1 and Figure 8.1 provide reference for ideal joint assess and treat, and it can be done with the assistance of range of motion and planes of movement respectively. video analysis and without expensive laboratory equipment. The aims of this chapter are to: Lower limb joint motion outline the basics of 'ideal' lower limb biomechanics The hip joinc is formed between the femoral head and acetabulum. The ball-and-socket structure of this joint explain the ideal biomechanics with running describe lower limb biomechanical assessment in the permits motion in all three planes. clinical setting The knee joinc is formed between the tibia! plateau and outline how to clinically assess footwear femoral condyles. Primarily a hinge joint, the knee allows review the best available evidence associating flexion and extension in the sagittal plane. The knee also biomechanical factors with injuries, as well as sharing permits some rotation in the transverse plane. This secondary clinical opinions as to which technical factors in sports motion is particularly important to allow the knee to lock contribute to specific injuries into an extended position for stance stability, and to unlock discuss how to manage biomechanical abnormalities when moving into flexion for shock absorption. The ankle joinc (between the shank and rearfoot) detected in the assessment explain normal and abnormal upper limb biomechanics. consists primarily of two articulations, the ca/ocrua/ joinc and the subcalar joinc (STJ). The talocrual joint is formed We address lower limb and upper limb biomechanics between the talus and the mortise of the tibia and fibula separately for the learner's convenience, but the experienced malleoli. Its axis of motion is predominantly in the frontal clinician will consider the close relationship between the plane which allows dorsiflexion and plantarflexion motion upper and lower limbs during a variety of functional tasks. in the sagittal plane (Fig. 8.2a and b).2 85 Table 8.1 A guide to lower limb joint ranges of motion when in neutral positions Hip Sagittal Supine Flexion = 120° Prone Extension = 20° Frontal Supine Abduction = 40°; adduction = 25° Transverse Supine/prone±hip Internal rotation = 45°; externa l rotation = 45 ° flexion/extension Knee Sagittal Supine Flexion = 135°; extension = 0 ° Frontal None Transverse Full extension None 70° flexion 45 ° rotation Foot and ankle (triplanar)' Sagittal Supine Plantarflexion = 45°; dorsiflexion = 20° Frontal Supination = 45-60°; pronation = 15-30° First metatarsophalangeal (MTP) Sagittal Supine Plantarflexion = 45°; dorsiflexion = 70° 'Refers to combined motion of the talocrual, subtalar, midtarsal and metatarsal break joints coronal (frontal) plane - sag ittal plane - -- tran sverse plane \ (a) (b) Figure 8.2 A xis of motion of the ankle joint (a) Superior Figure 8.1 Anatomical planes of the body view (b) Posterior view 86  The STJ is formed between the calcaneus and talus. weight-bearing. As the rear foot evens, the two axes align The three articular facets of the STJ allow for complex so they are more parallel, unlocking the foot and allowing triplanar motions of pronation and supination. The axis of it to conform to the surface and/or absorb the ground motion runs posteriorly and inferiorly in the sagittal plane reaction force (GRF). Conversely, as the rearfoot inverts, (40-50°), and laterally in the transverse plane (20-25 °)2 the two axes converge, locking the foot into a supinated (Fig. 8.3a-d). During pronation, the STJ axis provides position and allowing it to function as a rigid lever for primarily eversion, which is combined with dorsiflexion propulsion. 2 and abduction (Fig. 8.3d). During supination, the STJ axis provides primarily inversion, which is combined with plantarflexion and adduction (Fig. 8.3c). The midcarsal joinc is formed between the midfoot and rearfoot, and consists of two articulations, the calcaneocuboid joinc and the calonavicular joinc. These articulations provide two joint axes. The oblique axis allows large amounts of sagittal plane (dorsiflexion/plan- tarflexion) and transverse plane (abduction/adduction) motion, while the longitudinal axis allows small amounts of frontal plane (eversion and inversion) motion (Fig. 8.4a and b). Importantly, the orientation between these two axes allows the role of the foot to change during (c) (a) (b) (d) Figure 8.3 Axis of motion of the subtalar joint (a) Lateral view. Angle of inclination approximately 50° to transverse plane (b) Superior view. Angle between axis of motion of subtalar joint and longitudinal axis of the rearfoot is approximately 15° (c) Supination at subtalar joint with 20° calcaneal inversion (d) Pronation at subtalar joint with 10° calcaneal inversion 87 (a) (b) Figure 8.4 Oblique and longitudinal axis of midtarsal joint (a) Lateral view (b) Superior view The midcarsa/ (or Lisfranc) joincs are formed between the distal tarsal bones of the midfoot (cuneiforms and cuboid) and the five metatarsal bones (forefoot). The axis of motion for these joints runs primarily in the transverse plane in an oblique direction (Fig. 8.Sa and b). This leads primarily to sagittal plane motion (flexion/extension), although some frontal plane motion (eversion/inversion) does occur medially (adduction, Fig. 8.Sc) and laterally (abduction, Fig. 8.Sd). The firsc mecacarsophalangea/ joinc (MTPJ) is formed between the head of the first metatarsal and the base of the proximal phalanx. The primary motion that occurs at this joint is in the sagittal plane (flexion/extension) (Fig. 8.6). In particular, extension of this joint is essential to optimise function of the windlass mechanism (see below) during gait. (b) Ideal neutral stance position Figure 8.5 (a) midtarsal joints-the joints between To examine stance position, have the patient adopt a the distal tarsal bones of the midfoot (cuneiforms and normal, comfortable, standing posture. Ideal neutral cuboid) and the five metatarsal bones (forefoot) (b) The stance occurs when the joints of the lower limbs and metatarsal break (frontal plane). The axis of motion runs feet are symmetrically aligned, with the weight-bearing as shown (green rod) 88  transverse axis Figure 8.6 Motion of the hallux around the transverse axis of the first metatarsophalangeal joint (c) (d) Figure 8.5 (cont.) Frontal plane motion of the metatarsal break showing that the forefoot can (c) adduct and (d) abduct line passing through the anterior superior iliac spine, the patella and the second metatarsal (Fig. 8.7). When the feet are in a symmetrical position, the subtalar (talocalcaneal) joint is neither pronated nor supinated, and the midtarsal joint (talonavicular and calcaneocuboid joints) is maximally pronated so that the first and second metatarsal heads are in contact with the ground. The Figure 8.7 The alignment of the lower limb in neutral long axis of the forefoot through the second metatarsal is position. The weight-bearing line runs through the anterior perpendicular co the bisection of the heel (Fig. 8.8) and in superior iliac spine, patella and second metatarsal. The line with the tibia! cuberosity. The ankle joint is neither calcaneus is in line with the tibia, and the forefoot is plantarflexed nor dorsiflexed, and the tibia is perpendicular perpendicular to the calcaneus 89  biomechanical feature that distinguishes running from walking is the airborne or 'float' phase of running, where neither foot is in contact with the ground. 2 Additionally, vertical GRFs during running are double that of walking, 2 4 the pelvis is in greater anterior tilt, 5 and sagittal plane excursions of the knee and hip are increased. Ultimately, this leads to greater stress on structures of the lower limb. The heel strike pattern of running can be split into a number of phases (Fig. 8.9), each of which will be discussed below. Loading (heel strike to foot flat) With the leg swinging toward the line of progression, and the foot supinated, the rearfoot (heel) contacts the ground in slight inversion (0-5°). 2 · 6 -8 At heel strike, the pelvis is level, in slight anterior tilt (10°), and internally rotated; the hip is externally rotated (5- 10°) and flexed (20-30°); and the knee is flexed (10°). Due to the laterally directed line of the GRF produced by heel strike, a cascade of events occurs to assist shock absorption. First, the rearfoot begins to evert, accompanied by tibia! and femoral (hip) internal rotation, and hip adduction. This is combined with knee flexion, which peaks at around 45 ° as a result of the GRF line passing posterior to the knee joint.9 · 10 Each of these motions is controlled by eccentric muscle activity which helps to dissipate the GRF. In addition, there may be Figure 8.8 Normal relationship between the forefoot and contralateral pelvic drop, although this should be minimal rearfoot when the foot is in neutral stance (approximately 5°). 10 The gluteal musculature should actively control this motion and further dissipate the GRF. Initial rearfoot eversion also results in more parallel to the supporting surface in the sagittal and frontal plane. alignment of the midtarsal joints (i.e. calcaneocuboid and The knee is fully extended (but not hyper extended) and talonavicular), causing them to unlock. 2 Importantly, this in slight valgus alignment. The hips are in a neutral position allows the forefoot to make solid contact with the ground (neither internally nor externally rotated, neither flexed nor at foot flat 11 and allows the foot to adapt during loading extended). The left and right anterior superior iliac spines to potentially uneven or unstable terrain. 2 of the pelvis are level. A slight anterior tilt of the pelvis Although motions that comprise foot pronation is normal. More specific objective descriptions of ideal are normal, they should not be excessive or rapid (i.e. alignment are outlined in the assessment section. hyperpronation). Excessive motion will place strain on structures designed to control foot pronation, such as the 'IDEAL' BIOMECHANICS WITH plantar fascia, tibialis posterior muscle and intrinsic foot MOVEMENT-RUNNING musculature. 2 Excessive pronation also increases medial As injury mechanisms for many overuse injuries can be GRF, accentuating more proximal motion at the knee, associated with theoretically suboptimal lower limb hip and pelvis, and increasing load on ligamentous and biomechanics, the clinician must know how to assess muscular structures responsible for proximal control. 2 lower limb biomechanics during running. We focus The clinician should carefully note proximal motion first on the heel strike pattern of running as this is the during this early phase of stance. Excessive contralateral predominant pattern for the majority of runners.3 We will pelvic drop and/or hip adduction/internal rotation may then consider how biomechanics is altered when running increase strain on structures required to control it, such with a forefoot strike pattern. as the iliotibial band (1TB), gluteal musculature and tensor Although we focus on ideal running biomechanics, fascia latae (TFL) muscle. Additionally, this may also ideal walking biomechanics are similar to heel strike place increased or altered loading on the lumbar spine, running patterns outlined below. The most important tibiofemoral joint and patellofemoral joint (PFJ). Any 90 (a) Double Double support support (10%) (10%) Stance Swing 6(')%) I I I 10% 30% 50% 70% 85% Loading response Midstance I Term inal stance I Preswing Toe Initial swing Midswing Term inal swing off Strid e _ _ _ _ _ _ _ _ _ _ _ _ _ _... - - - - (100%) Heel strike Heel strike (b) Stride (100%) Double Double float float Stance Swing Absorption Propulsion Initia l swing Termin al swing Initia l Midstance Toe off Mid swing In itia l contact contact Figure 8.9 Gait cycle with phases and individual components (a) Walking (b) Running ADAPTED FROM DUGAN AND BHAT 2 excessive anterior tilting of the pelvis may place excessive Maximal foot pronation followed by maximal ankle strain on the lumbar spine and/or hamstring musculature, dorsiflexion should be reached immediately after and may impair gluteal function. the body's COM has passed anterior to the stance limb.11 Conversely, inadequate pronation or excessive supi- Peak rearfoot eversion should reach approximately 10°, 6 16 nation may lead to an excessive or prolonged laterally and peak forefoot abduction approximately 5°.6 The directed GRF, 2 resulting in a less mobile foot and poorer rearfoot then begins to invert and the forefoot adducts, shock absorption capacity. This may be associated with causing the foot to supinate, and the tibia and femur to lower limb stress fractures, 12 or increase the incidence of externally rotate. 11 This external rotation action is assisted lateral ankle sprain and chronic ankle instability. 13 14 by force transmission from the externally rotating pelvis, which results from momentum of the swinging contra- Midstance (foot flat to heel off) lateral limb. The beginning of midstance is indicated by the forefoot making There are a number of things for the clinician to contact with the ground, normally in a neutral transverse consider during this phase. Excessive pronation, or plane position (i.e. not abducted or adducted).6 Lower limb delayed/failed transition from shock absorption to biomechanical function during midstance involves a transition propulsion actions by the lower limb, may be detrimental from biomechanics required for shock absorption following to a number of structures. Firstly, this will place excessive loading, to biomechanics required for propulsion. During strain on structures responsible for controlling pronation this time, the ankle moves towards maximal dorsiflexion and may increase the risk of conditions such as plantar (approximately 20°) to allow forward motion of the tibia fasciopathy, Achilles and tibialis posterior tendinopathies, and the centre of mass (COM) to pass over the stance Ieg. 15 proximal tibia! periostitis, or tibia! stress fractures Excessive ankle dorsiflexion can lead to increased strain on the due to excessive pull of the tibialis posterior and long plantar fascia, Achilles tendon, and associated gastrocnemius flexors. Also, continued instability of the foot may lead and soleus musculature. At the same time, the hip and knee to development of first MTPJ abnormalities, including are moving from flexion towards extended positions, assisting hallux valgus, sesamoid pain and/or excessive interdigital forward motion of the body's COM. compression (Morton's neuroma). If left untreated, 91 over time this instability may also lead to metatarsal or the foot is supported by the windlass mechanism, that is, sesamoid stress fractures. increased tension of the plantar fascia due to extension of More proximally, excessive or prolonged pronation the metatarsals, which pulls the calcaneus and metatarsal may also result in abnormal transverse and frontal plane heads together (Fig. 8.10). 2 By toe off, the rearfoot should motion at the hip and knee due to a delay in external be inverted to approximately 10°, and the forefoot rotation. Ultimately, this can place excessive strain on adducted approximately 5°.6 many structures such as the PFJ, patellar tendon (both Failure of normal propulsion will cause an inefficient conditions discussed in Chapter 36), 1TB (Chapter 37), and gait pattern. This can limit performance and predispose to musculature that control this motion. Conversely, the same injury for several reasons. First, the peroneal musculature proximal anomalies may result due to inadequate pelvic and may be forced to work harder to stabilise the medial and hip control. The source of the biomechanical dysfunction lateral columns of the foot which can lead to peroneal may need to be determined through further structural and tendinopathy and/or stress fracture of the fibula. functional tests (see assessment section below). Second, impaired supination may lead to toe off via the lateral rays instead of the first ray. This may compress Propulsion (heel off to toe off) the transverse arch of the foot excessively, and lead to Following heel off, the foot continues to supinate. interdigital nerve compression (Morton's neuroma) and Importantly, as this occurs, inversion of the rearfoot risk of lateral forefoot stress fracture. causes the transverse tarsal joint axes to converge.2 Third, reduced propulsion from the stance limb may This convergence of joint axes causes the midfoot to increase reliance on the swing phase to produce forward lock into position, creating a rigid lever.2 Concurrently, momentum. To achieve this, the hip flexors, rectus femoris the stance limb continues to externally rotate, the hip and iliopsoas will generate more rapid hip flexion, increasing reaches maximal extension of between O and 10°, 5 · 15 17 the potential for tendinopathies. Additionally, to compensate and the knee flexes once more due to hamstring muscle for impaired propulsion, pelvic and trunk rotation may contraction. 15 17 Additionally, acceleration of the stance increase, leading to increased strain on spinal structures. limb is provided through plantar flexion at the ankle, produced by the gastrocnemius and soleus complex.18 This Initial swing same gastrocnemius and soleus activity, along with the Following ipsilateral toe off, the body is thrust into the tibialis posterior and intrinsic foot musculature activity, first 'float' phase where neither limb is in contact with continues to actively assist supination of the foot, and the ground. Rectus femoris and iliopsoas muscle activity maintain its function as a rigid lever.2 Passively, rigidity of continue the forward momentum of the now swinging Figure 8.10 The windlass mechanism comes into play after heel off. Metatarsal extension increases tension on the plantar fascia, and forces the transverse tarsal joint into flexion which increases stability at push off 92 limb. 19 As the limb advances, the pelvis moves with it, from the line of progression in walking. Abducted gait thrusting the hip into abduction and external rotation, describes an angle of gait greater than 10°. The angle of which is in turn controlled by the hip adductors. 19 The gait reflects the hip and tibia) transverse plane positions. tibialis anterior contracts to begin dorsiflexing the foot The base of gait is the distance between the medial in preparation for terminal swing. 19 While these motions aspect of the heels (Fig. 8.11). A normal base of gait is continue, they are aided by the addition of a new stable approximately 2.5-3 cm. support when the contralateral limb strikes the ground Changes from the normal angle and base of gait may be and commences its own loading phase. Continuation of secondary to structural abnormalities or, more commonly, normal swing at this time relies on the ability of the as compensation for another abnormality. For example, a contralateral gluteal musculature to dissipate the GRF wide base of gait may be necessary to increase stability. produced by this event and prevent the pelvis dropping As running velocity increases, the angle and base of gait on the swing side. Failure to do so will increase the work decrease. With faster running, the angle of gait approaches required by the hip and knee flexors to clear the swinging zero and foot strike is on the line of progression. This limits limb, possibly leading to overuse injury. deviation of the COM as the lower limbs move beneath the body, thus allowing more efficient locomotion (Fig. 8.12). Terminal swing Following contralateral toe off, the body is thrust into the second 'float' phase. During this time the ipsilateral swinging hip reaches maximal flexion (approximately 30°),5 9 before being brought under control by the hamstring and gluteal musculature. 19 The same hamstring activity slows the rapidly extending knee in preparation for heel strike. At the same time, the hip adductors, which have been working eccentrically to control abduction of the swinging limb, begin to work concentrically to adduct the hip and bring it toward the midline.19 Angle and base of gait The angle of gait is the angle between the longitudinal bisection of the foot and the line of progression (Fig. 8.11). The normal angle of gait is approximately 10° abducted Line of progression - (a) Line of progression Figure 8.11 The angle of gait is the angle between (a) the (b) long axis at the foot and (b) the line of progression. (c) Base of gait is the distance between the medial aspects of the heels Figure 8.12 Angle and base of gait (a) Walking (b) Running 93 Landing point relative to centre of mass reduce their excursions in all three planes with increased Greater distance between foot strike point and COM (i.e. velocity. 22 This indicates the need for stiffer joint overstride) has been reported to increase lower limb joint structures with increased speed and a greater demand on loads,20 and as a result is thought to increase the risk of intrinsic foot musculature control. 22 running injury development. When measuring this clinically, In slower running, the stance phase takes longer than we suggest this distance should not exceed more than one the swing phase. As running speed increases, stance phase third of a foot length (Fig. 8.13), with greater than a foot and flight phase times approach each other until the length considered a marked overstride. During sprinting, the stance phase becomes shorter than the swing phase in foot should land almost directly under the COM. sprinting (Fig. 8.14). 2 Additionally, as running velocity increases, foot strike Influence of gait velocity patterns may be altered. As mentioned previously, foot Increased gait velocity influences a number of strike patterns are similar between slow running and walking for most individuals (Fig. 8.15). During faster biomechanical factors. As gait velocity is increased, running (striding), the foot may strike with the heel and greater emphasis is placed on the swinging actions of the upper limbs, trunk and lower limbs to produce forefoot simultaneously prior to heel off (midfoot strike), forward momentum.2 This difference has significant or may strike with the forefoot initially followed by heel lowering to the surface prior to heel off (forefoot strike). implications for the flexibility and eccentric muscle control requirements of these structures (e.g. ipsilateral In sprinting, weight-bearing is maintained on the forefoot hamstrings strain during late swing). Greater excursion from contact to toe off, although the heel may lower to the of the proximal joints (knee, hip and pelvis) also occurs supporting surface at midstance. In some individuals, this with increased velocity, placing increased reliance on pattern can commence even at slower running speeds, or eccentric muscle control. 19 21 At the foot and ankle, the immediately upon initiation of a run. In particular, some bones making up the rearfoot, midfoot and forefoot all habitual barefoot runners often have a natural forefoot strike pattern regardless of velocity. 3 Comparing heel and forefoot strike patterns Changing from a heel strike to a forefoot strike pattern has significant implications for lower limb biomechanics and assessment. This has become particularly important Walking 'k \iiit~ ~)r,:;, Jogging "k It Distance running jp \It -:W u Figure 8.13 Heel to COM distance at initial contact during Figure 8.14 Pattern of the stance phase during different running 20 speeds of walking and running 94  di(,\ {:fr Follow-! ro swing phase (left leg) Stance phase _ Heel strike c-~ Forwa rd swing Midstance 1W Toe off Foot descent (right leg) Figure 8.15 The swing and stance phases of running to clinical practice with the recent popularity of Born to LOWER LIMB BIOMECHANICAL Run 23 and many runners choosing to transition from a ASSESSMENT IN THE CLINICAL SETTING habitual heel to a forefoot strike. Firstly, forefoot strike This section aims to help the junior clinician develop a patterns result in slight plantar flexion of the foot at routine for efficient lower limb biomechanical assessment. impact, followed by dorsiflexion as the heel lowers to There is no single best way to assess biomechanics and the ground. 2 This means that the ankle joint is more the experienced clinician will vary his or her assessment compliant and able to absorb GRF in the sagittal plane, depending on the clinical presentation. and can lead to a reduction in vertical GRF and loading For this example, consider the patient to have rates following foot strike.3· 6 Additionally, forefoot patellofemoral pain- a condition that warrants assessment striking has also been reported to reduce knee and hip of the entire kinetic chain. joint loads, and these changes are often used to justify transition toward a forefoot strike for hip and knee PRACTICE PEARL injuries.24 However, concurrent increases to joint loads at the ankle indicate potential detrimental increases to Two guiding principles will help with the efficiency of tissue stresses distally, 24 which fits with many anecdotal the office assessment and ensure it is appropriately reports of Achilles tendinopathy, plantar fasciopathy and comprehensive. metatarsal stress fractures as a result of transitioning from 1. Examine from distal to proximal (start at the foot and heel to forefoot strike. then examine proximally to the pelvis and trunk). 2. Examine the patient in 'static stance' first Influence of fatigue on running before increasingly challenging him or her with biomechanics 'functional' tests before moving to fully 'dynamic' Some runners will report pain that only occurs following or 'sport-specific' tests as appropriate (see prolonged activity. For example, an individual with Fig. 8.16 for the concept of the hierarchy). These patellofemoral pain (Chapter 36) may report no pain during terms are explained below. the early stages of a run, but cease running due to severe pain after five kilometres. This can make clinical assessment Thorough biomechanical assessment may require the difficult, since the condition may result from suboptimal patient to stand, walk, run, land on two feet and land on biomechanics that only occur with fatigue. For example, one leg only. Assessment during 'function' (playing sports, excessive hip adduction during running in the individual executing certain sporting activities such as a kick or a with patellofemoral pain may occur due to poor gluteal pirouette) may also be relevant. muscle endurance. Therefore, the clinician should evaluate We explain each of these steps in the order that many functional biomechanics both at baseline and following experienced clinicians perform the assessment. The major fatigue and/or onset of pain. In the clinical setting, this elements in the assessment are: means scheduling the appointment so that the patient can structural (static) biomechanical assessment (Fig. 8.17a-g) be seen before and immediately after a run, or having them functional lower limb tests- single-leg stance, heel raise, run to a fatigued state before attending the clinic. squat and landing (Fig. 8. l 8a-g) 95  ACTIVITY Static A good starting place. The patient stands in a comfortable position, stance weight centrally distributed over both feet (see also Fig. 8.17a-g). This refers to a group of simple movements in isolation- Simple single-leg standing, single-leg heel raise, sing le-l eg squat, step functional down, hopping and landing (see also Fig. 8.18a-g). Thi s refers to activities such as running. Thi s may need to be done Dynamic outside the office on an adjacent tr ack, park or car park depending movements on w hat is availab le. If the ath lete is a basketball player, ballet dancer, or pole vau lter (for Sport-specific example), the clinician may also need to observe the athlete activity performing sporting activities that are relevant to the presenting comp laint. Figure 8.16 An overview to guide lower limb biomechanical assessment (See also Figures 8.17 and 8.18.) assessment of a patient's running biomechanics Foot ('dynamic assessment') Inspect the foot subjectively (does it look abnormal?), detailed sport-specific tests as indicated by the above quantify posture using the six item Foot Posture Index tests and the clinical presentation. (FPI) below and also pay attention to first MTP range of motion (Fig. 8.17b). Structural ('static') biomechanical assessment Foot Posture Index The clinician performs the assessment of static stance Quantify standing foot posture objectively with the FPI, by critically viewing the foot, ankle, knee and pelvis a test that reflects foot posture at the rearfoot, midfoot (Fig. 8.17a). and forefoot, as well as an overall impression of foot 96  (b) Figure 8.17 Static assessment of the lower limb (a) With the patient in this comfortable position, static stance examination begins at the foot. The examiner then assesses the ankle, knee and hip/ pelvis (b) Jack's test for first MTPJ dorsiflexion range of motion. Normal range of motion is approximately 50° relative to the floor (a) The Foot Posture Index 26-a rapid, quantitative measure of static foot biomechanics Each of the six items in the FPI is scored as -2 (highly Bulging in the region of the talonavicular joint (TNJ) supinated), -1 (supinated), O (neutral), + 1 (pronated) or +2 A neutral score is given if the sk in immediately superficial (highly pronated); this leads to sums between - 12 (highly to the TNJ is fl at. If the TNJ is bulging , a pronated score is supinated) and + 12 (highly pronated). 26 given (+2 defined by marked bulging) and if the TNJ area is concave (indented) a supinated sco re is given (-2 defined by Talar head palpation m arked concavity). The talar head is palpated on the anterior aspect of the ankle. If the head can be felt equally on the medial and lateral Height and congruence of the medial longitudinal arch side, a neutral score (0) is given. If greater prominence is A neutral score is given if the arch shape is uniform and felt medially, a pronated score is given (+2 defined by only similarly shaped to the circumference of a circle. If the arch is medial prominence felt) and if greater prominence is felt flattened and lowered, a pronated score is given (+2 defined laterally, a supinated score is given (-2 defined by only lateral by the mid-portion of the arch making contact with the fioor). If prominence felt). the arch is high , a supinated score is given (-2 defined by an acutely angled posterior end of the arch). Supra and infra lateral malleolar curvature A neutral score for this item is given if the curves above Abducti on/adduction of the forefoot on the rearfoot and below the lateral malleolus are equal when viewed A neutral score is given when the forefoot can be seen posteriorly. If the curve above the malleolus is flatter, a equally on the medial and lateral side when viewed from pronated score is given (+2 defined by completely flat) and if behind the axis of the rearfoot. If more of the forefoot is visible the curve below the malleolus is flatter, a supinated score is laterally than medially, a pronated score is given (+2 defined given (-2 defined by completely flat). by only lateral forefoot visible) and if more of the forefoot is visible medially than laterally, a supinated score is given Calcaneal frontal plane positi on (-2 defined by only medial forefoot visible). A neutral score is given if the rearfoot is perpendicular to the floor. A more valgus rearfoot relative to the floor is given a The total FPI score for the normal healthy population is 2.4 pronated score (+2 defined by >5°) and a more varus rearfoot (i.e. slightly pronated). 28 Thus, scores of Oto +5 are considered relative to the fioor is given a supinated score (-2 defined neutral. A score of +6 to +9 is considered pronated, ~+ 10 highly by > 5 °). pronated, -1 to -4 supinated and -5 to -12 highly supinated. 97 type. It requires no equipment and takes approximately motion may result from the presence of a valgus aligned 2 minutes to complete.25· 26· 27 forefoot. 33 Both these structural issues can be corrected Additional background information about the FPI, using orthoses, taping and/ or corrective exercise. including definitions and pictures of various foot types for each item, are shown in the user guide and manual. 25 Note Ankle dorsiflexion that, as with any clinical skill, training and experience are Accurate ankle dorsiflexion in weight-bearing using an important. The clinician should rate at least 30 individuals inclinometer provides a more useful measure of range with a broad range of foot types before applying the FPI of motion at this important joint than does a rough clinically.29, 30, 3i assessment when the patient is lying on a treatment couch. This ankle biomechanical assessment is best done Jack's test for first metatarsophalangeal joint with the knee both extended and flexed (Fig. 8.17 c (MTPJ) range (plantar fascia integrity) and d). Normal ankle dorsiflexion range with the knee The clinician can rapidly assess the first MTPJ and also the flexed is 45° and with the knee extended is 40°.30 We integrity of the plantar fascia using 'Jack's test' (Fig. 8. l 7b).32 recommend that clinicians have an inclinometer readily The normal range of first MTPJ dorsiflexion motion available (Fig. 8.17c and d)- it adds a great deal of accuracy should be around 50° relative to the floor. As the first ray to measurements and reduces assessment time. dorsiflexes, tightening of an intact plantar fascia should An alternative way of quickly assessing weight-bearing cause the rearfoot to invert. If the rearfoot does not move, ankle dorsiflexion is to have the patient perform the it suggests poor plantar fascia integrity which can result 'knee-to-wall' test (Fig. 8. l 7e). This provides an efficient in inadequate supination during the propulsive phase of outcome measure for ankle dorsiflexion range when gait. Additionally, increased resistance to or a reduction in gastrocnemius tightness is not a concern and this can be (c) (d) Figure 8.17 (cont.) (c) Assessing ankle dorsiflexion in weight-bearing with the knee extended (d) Assessing ankle dorsiflexion in weight-bearing with the knee flexed 98  Assessment of tibiofemoral alignment at the knee Tibiofemoral joint alignment may reflect genu varum or valgum (Fig. 8. l 7f and g). This can also be measured using an inclinometer, which compares favourably to the gold standard radiographic measure. 34 Leg length assessment Discrepancies in leg length are extremely common, existing in up to 70%of the normal population. 35 Nevertheless, leg length discrepancy has long been thought to be a risk factor for a range of musculoskeletal conditions, including low back pain, hip and knee osteoarthritis, and lower limb stress fractures. 35 36 Laboratory studies have shown that leg length differences alter the distribution of mechanical stress within the body, particularly by increasing the magnitude of forces through the shorter limb. 37 However, prospective risk-factor studies in athletes are lacking and what constitutes a clinically significant leg length difference remains unknown. Subsequently, the extent to which leg length differences should be (e) Figure 8.17 (cont.) (e) The knee-to-wall test. It is useful to have a line on the floor that continues up the wall. The patient lines up their second toe and mid-calcaneus on the horizontal line and lunges their patella toward the vertical line. This minimises the likelihood of going into pronation to achieve greater range of motion (ROM). The distance from the wall to the second toe is recorded PRACTICE PEARL If ankle dorsiflexion range differs in knee extension and flexion by more than 5°, it suggests there is limitation of dorsiflexion with the knee extended; this points to gastrocnemius tightness. If foot pronation is excessive to achieve normal ankle dorsiflexion range (i.e. 45°) with the knee bent, excessive pronation may be occurring during functional activities to achieve full functional movement (e.g. when running). particularly useful following lateral ankle sprain. With the knee-to-wall test, clinicians can determine whether there are side-to-side differences or if ankle dorsiflexion is restricted. 'Normal' values will vary depending on the size (f) of the patient and their sport-specific demands, but, as a general rule of thumb, the distance from the wall to the Figure 8.17 (cont.) Static assessment of the lower limb- second toe should be greater than 8- 10 cm. alignment at the knee (f) Genu varum 99  Possible mechanisms that underpin common clinical observations are shown in Table 8.2. Functional lower limb tests The next step is to assess simple functional movements. The patient should do these tests both with and without sporting footwear where appropriate. This will help the clinician determine whether the individual's footwear is detrimental, beneficial or has no effect on functional biomechanics. Single-leg stance with progressions The single-leg stance test begins to challenge lower limb balance and proprioception (Fig. 8.18a). Inability to maintain the single-leg stance position is likely to carry over to suboptimal biomechanics during sporting activity. The patient performs this test with (i) eyes open, (ii) eyes closed and (iii) challenged further by also performing a single heel raise. Depending on the balance requirements for the individual, once balance can be maintained in single-leg stance for at least 10 seconds, balance can be assessed using more challenging activities, including variations in surfaces and ability to adapt to internal and external perturbations. (g) Figure 8.17 (cont.) (g) Genu valgum corrected in athletes remains a source of controversy, with opinions ranging from 3 mm to 22 mm.38 We recommend that clinicians take a 'treatment direction test' approach (see below) and adopt corrections if they substantially change symptoms. Leg length can be measured in a variety of ways, including clinical measures using a tape measure in standing (anterior superior iliac spine or ASIS to floor) and in supine (ASIS to medial malleolus). However, these methods may be inaccurate, with reports of poor inter- and intra-rarer reliability and errors of up to 20 mm compared to radiographic imaging. 38 There are a number of radiographic techniques to evaluate leg length differences, including magnetic resonance imaging (MRI), computed tomography (CT) 'scanograms' and standing full leg radiograph. Each of these methods has demonstrated high accuracy with average errors of less than 2 mm. 39 Summary of static assessment (a) The 'static' biomechanical assessment of the foot, ankle and knee provides a substantial amount of valuable clinical Figure 8.18 Functional assessment of the lower limb. information and can be completed within 5 minutes. (a) Single-leg stance to evaluate alignment and control 100 Table 8.2 Common lower limb biomechanical observations, possible mechanisms and confirmatory assessments.. - Excessive or asymmetrical pelvic Inadequate ROM (hip) Clinical ROM tests with inclinometer (Chapter 31 ); or trunk movement (frontal, figure '4' test transverse, sagittal planes) Inadequate strength (abdominals, lumbopelvic Manual muscle tests muscles, hip abductors) Altered neuromotor control (hip abductors, Biofeedback lumbopelvic muscles) Decreased muscle length (hamstrings, rectus Muscle length tests abdominis, rectus femoris) Lumbar spine/sacroiliac joint stiffness/pain Joint palpation Increased hip adduction/femoral Structural (femoral anteversion) Radiographic: MRI, X-ray internal rotation Clinical assessment Inadequate ROM (hip) Clinical ROM tests with inclinometer (Chapter 31 ); figure '4 ' test Inadequate strength (hip external rotators, Manual muscle test (Chapter 31) or hand-held abductors) dynamometry Altered neuromotor control (hip external Biofeedback rotators , hip abductors) Increased apparent knee valgus Structural (genu varum, tibial varum , coxa Imaging: MRI, X-ray varum) Clinical assessment: goniometer, inclinometer Inadequate ROM (hip) ROM tests: clinical (Chapter 31) inclinometer; figure '4' test Inadequate strength (hip external rotators, hip Manual muscle test (Chapter 31) or hand-held abductors, quadriceps, hamstrings) dynamometry Active gluteal and tensor fasciae latae trigger points Altered neuromotor control (hip external Biofeedback rotators , hip abductors, lumbopelvic muscles) Active gluteal and TFL trigger points Ankle equinus Inadequate ROM (ankle) ROM tests Tight gastrocnemius or soleus ROM tests with knee flexed and extended (Fig. 8.17c and d) Excessive or prolonged foot Pronated foot type FPI pronation Impaired windlass mechanism Jack's test (Fig. 8.17b) Tibialis posterior weakness Single-leg heel raise; manual muscle test; inability to form arch Ankle equinus Ankle dorsiflexion measures Leg length discrepancy (structural or Clinical measurement and radiographic imaging functional) Excessive or prolonged foot Supinated foot type FPI supination Chronic ankle instability Ankle ligament integrity tests Leg length discrepancy (structural or Clinical measurement and radiographic imaging functional) Reduced propulsion Impaired windlass mechanism Jack's test (Fig. 8.17b) Tibialis posterior weakness Single-leg heel raise; manual muscle test; inability to form arch Pronated foot type FPI ROM = range o f motion ; FPI = foot pronatio n index 101 Single-leg heel raise (with a focus on tibialis to evaluate the capacity of the intrinsic muscles of the posterior function) foot and tibialis posterior to control the foot during stance Tibialis posterior is an under-recognised contributor in gait. The patient is instructed to gently lift up the to normal lower limb biomechanics- it is particularly inside arch while pushing the first metatarsophalangeal important for control of foot pronation and helps stabilise joint into the ground. The clinician can monitor the plantar arch during activity. Through its attachments performance by placing a finger underneath the joint to to the navicular, cuneiforms, cuboid and bases of the ensure sufficient downward pressure. The patient should second to fourth metatarsals, tibialis posterior inverts be able to maintain this for 10 seconds. As above, the the subtalar joint. It is a primary dynamic stabiliser of procedure provides a therapeutic exercise when deficits the foot against eversion forces and is also important for are observed. Note that the arch form test would not propulsion. necessarily be part of a routine rapid biomechanical A simple functional test, the single-leg heel raise, tests assessment- it provides additional information if this is the ability of tibialis posterior to re-supinate the foot warranted (e.g. if the patient demonstrates excessive or during propulsion of gait (Fig. 8.18b). Tibialis posterior rapid foot pronation). muscle weakness will manifest as an inability to rise up through the medial aspect of the foot and invert the Single-leg squat to assess knee, hip and trunk rearfoot toward the end of the heel raise. (Note that muscle function the same procedure can be prescribed as a therapeutic The continuum of activities from single-leg squat (at exercise when deficits are observed- this may initially approximately 45° knee flexion), step down, hopping, to require the use of support or starting in bilateral stance). landing, provides a logical progression to the lower limb If tibialis posterior problems or excessive dynamic foot biomechanical assessment. There are many variations pronation are suspected, the 'arch form' test can be used for performing a single-leg squat, including depth (knee flexion angle), arm position (crossed, hands on hips, no constraints) and posture of the unsupported leg (in front, behind) (Fig. 8.18c and d). Clinicians should ensure that they always use the same technique. Assessment of hip and trunk function Five main observations may indicate altered hip or trunk muscle function. The first four can be observed from in front of the athlete and the fifth is an overall assessment. 40 Trunk Trunk lean (and/or rotation) toward the stance leg may be an adaptation to altered control of hip abduction/rotation or trunk lateral flexion/rotation. This may be observed as a more lateral position of the shoulder, relative to the hip (Table 8.2, Fig. 8.18d). Pelvis and hip Altered control of hip abduction/rotation or trunk lateral flexion/rotation may present as either (a) inability to maintain a level pelvis or (b) ipsilateral shift of a level pelvis. Both presentations may be observed as a lateral hip (ASIS), relative to the knee (hip adduction) and may also be referred to as a Trendelenburg sign' (Table 8.2, Fig. 8.18d). (b) Knee Figure 8.18 (cont.) (b) Single-leg heel raise. Look for signs Does the centre of the knee remain over the centre of the of tibialis posterior weakness, including (i) inability to rise foot? If the knee deviates toward a more medial position through the medial arch or (ii) failure of the heel to invert (relative to the foot), this is an indication of increased 102  (c) (d) Figure 8.18 (cont.) Single-leg squat (c) Good form (d) Poor form hip internal rotation and/or adduction and appears as test so that healing tissue does not receive excessive stress. an apparent knee valgus posture. Increased hip internal It may also be important to evaluate landing performance rotation/adduction may result from altered control of hip both pre- and post-exercise, since fatigue is associated muscles (e.g. hip external rotators) (Table 8.2). with increased knee abduction and reduced knee flexion during landing. 41 42 Overall impression We suggest evaluating both double-leg and single-leg An individual with altered hip/trunk muscle function may landing using a drop landing assessment from a 30 cm exhibit global signs, such as poor quality of movement/ high platform (Fig. 8.18e-g). The clinician should observe coordination, inability to squat to the desired depth, or the landing pattern for signs of reduced knee and hip inability to control speed, depth and balance. flexion and/or an abnormally erect landing posture. Apparent knee valgus is another movement to observe. Landing-specific considerations Maximum knee valgus should reach approximately 10° There are a number of ways to evaluate single-leg and for females and 5° for males for both tests from this double-leg landing biomechanics in the clinical setting. height. 43 Excessive valgus and/or the presence of a heavy The clinician should determine what is appropriate taking landing pattern involving minimal knee, hip and trunk into account the individual's sporting requirements and flexion may increase the risk of future knee injury or injury history. It may be more appropriate to evaluate re-injury, such as non-contact anterior cruciate ligament single-leg landing if a higher-functioning athlete presents injuries. with a lower limb injury. The single-leg landing may be As with running and squatting assessment, video the best way to identify biomechanical deficiencies such footage can be used for more in-depth analysis of double- as increased knee abduction, and decreased knee, hip and leg and single-leg landing. The clinician can use slow- trunk flexion. motion replay and computer software packages to gain a Conversely, in individuals recovering from injury and/ more accurate picture of the degree of knee valgus during or surgery, double-leg landing may be a more appropriate landing. 103  (e) (g) Dynamic movement assessment (e.g. running biomechanics) A key to clinical biomechanical assessment is careful observation of functional movement. Running is a component of many sports and the clinician should have an effective method to assess for biomechanical problems associated with running. As a clinician, look for obvious deviations from the ideal running pattern, and use this to guide further assessment and treatment decisions. Common deviations and possible implications to injury are outlined in the 'ideal' biomechanics with movement- running' section. If possible, observe athletes participating in their sport. If necessary, sport-specific skills can be broken down into component movements to simplify observation in the clinic. Furthermore, functional clinical tests outlined in this chapter may provide insight into biomechanics during more sport-specific tasks when they cannot be evaluated in the clinical setting. For example, excessive Figure 8.18 (cont.) (e) Starting position for single-leg landing (f) View from the front (g) View from the side (f) 104 hip adduction during the completion of a single-leg assessment- it will vary by clinical specialty (e.g. squat may be indicative of excessive hip adduction physiotherapy, podiatry, medicine, exercise physiology). during running and landing. Also, the clinical problem will influence the order of the To detect sub-optimal biomechanics with the naked assessment and the relative emphasis on various elements. eye takes years of training and experience. Video analysis In this introductory chapter, we have focused on general can provide valuable information from multiple views lower limb biomechanics. This would apply, for example, and assist the clinician greatly. This is usually done by to a patient with patellofemoral pain. The assessment may having the patient run on a treadmill. Reflective markers differ for other conditions. can be added to identify anatomical landmarks and bony alignment. Video footage can then be slowed on a replay CLINICAL ASSESSMENT OF and this may reveal otherwise hidden abnormalities. A FOOTWEAR-THE FOOTWEAR number of freely available computer software programs ASSESSMENT TOOL can also assist with this analysis. Examples include Footwear assessment is a vital component of the lower Hudl and Kinovea. The source of any biomechanical limb biomechanical evaluation. The Footwear Assessment abnormalities may be further investigated by a thorough Tool is a freely available six item template to guide the clinical assessment. clinician when assessing footwear. 4 4 The tool focuses on general structure and fit (Table 8.3), motion control Sport-specific assessment properties and wear patterns. A detailed sport-specific assessment may help identify Motion control is particularly important for excessive factors causing or contributing to injury. It is therefore pronators. Footwear properties that influence motion important that clinicians understand the normal bio- control include heel counter stiffness, midfoot torsional mechanics of their patient's sport, as well as the normal and sagittal stability, and type of fixation (e.g. lacing). range of variability between athletes. We encourage These properties can be quantified using the motion clinicians to collaborate closely with coaches and sport control properties scale outlined below (Table 8.4).4 4 scientists when performing sport-specific assessments. Scores range from O to 9, with 9 indicating the highest Sport-specific biomechanical issues thought to be level of motion control. associated with injury are examined in Chapter 9 for a The wear pattern of a shoe can provide insight into range of different sports. the biomechanics of gait. Medial tilt of the upper, medial compression of the midsole and greater medial than Summary of the lower limb biomechanical lateral wear of the outsole (Fig. 8.19) indicate excessive assessment pronation. Lateral tilt of the upper, lateral compression of To iterate how we opened this section, there is no the midsole, and greater lateral than medial wear of the single way to perform the lower limb biomechanical outsole reflect excessive supination. Table 8.3 Footwear assessment-general structure and fit Fit Inadequate width or depth Joint compression (e.g. Morton's neuroma) Restriction of normal foot function Pitch Difference between heel height and Small pitch may not be suitable for someone with ankle forefoot height (typical range 0-14 mm) equinus Large pitch may increase likelihood of overstride and impair attempts to transition to midfoot or forefoot strike Last Straight last (0-5 °) Accommodates a pronated foot Curve last(> 15°) Accommodates a supinated foot Forefoot sole flexion point Shou ld line up with the first MTPJ If too proximal, shoe stability may be impaired. If too distal , normal sagittal plane motion of the first MTPJ may be impaired, which can be problematic in the presence of poor intrinsic foot and tibialis posterior strength and function 105 Table 8.4 Motion control properties scale44 Fixation (upper to foot) None Alternative to laces Laces (at least 3 eyelets) (e.g. strap, Velcro, zip) Heel counter stiffness No heel counter Minimal Moderate Rigid Midfoot sagittal stability Minimal Moderate Rigid Midfoot torsional stability Minimal Moderate Rigid Minimal = >45°; moderate =