MusculoSkeletal Exam

Talus

Figure 14.2 Pronation (plantar medial rotation) of the talus results in internal rotation of the leg and supination torque of the middle of the foot.

accommodate medial rotation. This medial rotation is termed pronation. Efficient locomotion requires the simultaneous occurrence of both talar functions. The lower extremity must accommodate the internal rotational torque that subtalar pronation creates. It must transmit this force proximally through the rigid ankle mortise during gait. This torque is most efficiently accommodated by a complex combination of knee flexion and internal rotation of the entire lower extremity through the ball-and-socket mechanism of the hip joint. Such a compensatory motion has the potential to place excessive stresses at the structures proximal to the ankle and foot, such as the patellofemoral articulation (Figure 14.2).

Closer inspection of the ankle and foot shows that the body of the talus is supported by the calcaneus, and these bones diverge at 30 degrees in both the coronal and sagittal planes. The result is that the head of the talus is supported by soft tissues (the talocalcaneonavicular or “spring” ligament, and the posterior tibialis tendon). As such, in the presence of soft-tissue or generalized ligamentous laxity or muscular weakness, the head of the talus can experience excessive plantar flexion. This excess movement will force the

Chapter 14 Gait

calcaneus laterally, with an eversion of the hindfoot. During weight bearing, this displacement will force internal rotation of the entire lower extremity about the ball-and-socket articulation of the hip. If unchecked, this situation will create excessive loading at several points along the lower extremity:

1valgus and medial rotation of the first metatarsophalangeal joint (leading to hallux valgus and bunion formation);

2excessive stretching and strain of the tibialis posterior muscle and tendon (shin splints);

3increased internal rotation of the knee, resulting in an apparent increased “Q angle,” lateral patellar subluxation stress, increased medial retinacular tension, increased lateral compression loading of the patellofemoral facet, and increased tension in the popliteus muscle; and

4increased internal rotation of the hip, increased tension/stretch loading of the external rotators of the hip (producing piriformis syndrome and sciatic nerve irritation [sciatica]).

As discussed earlier, situations that create excessive

repetitive loading may lead to breakdown of tissues and structure (the “vicious cycle of injury”). Each of the pathological conditions listed above is a potential consequence of insufficient subtalar support and resultant excessive pronation, which has produced a biological system failure.

There are several clinical examples of biological system failure secondary to excessive subtalar pronation. The swelling of the medial capsule and resultant accumulation of hard and soft tissues about the first metatarsophalangeal joint of the foot, known as a bunion, is the direct consequence of excessive loading stresses at the medial aspect of the first metatarsophalangeal joint (Figure 14.3). The unsuccessful attempt of the tibialis posterior muscle-tendon to support the subtalar arch results in excessive stretching and stressing of that muscle-tendon unit. This explains the appearance of pain in the posteromedial aspect of the leg and ankle (shin splints) at the location of the muscle’s origin, in an insufficiently conditioned runner. The hip, as a ball-and-socket articulation, provides little resistance to inward rotational torques. As such, inward rotation of the entire lower extremity forces the axis of the knee to rotate medially. This inward rotation of the knee will accentuate the valgus alignment of the knee as it flexes. This combination of medial or internal rotation and flexion of the knee creates and increases (apparent) valgus angulation of the knee joint. This valgus in turn creates a greater

Figure 14.3 Hindfoot pronation may result in valgus stressing of the first metatarsophalangeal joint. Chronic valgus stress can result in the formation of a swelling (bunion) and angulation of this joint (hallux valgus deformity).

lateral displacement vector on the patellofemoral mechanism with quadriceps contraction (Figure 14.4). This occurs because the direction of the quadriceps pull attempts to resolve the Q angle to a straight line of 180 degrees. This increased laterally directed vector force on the patella has a direct consequence on the longevity and attrition of patellar articular cartilage. It also creates excessive tension within the medial peripatellar soft tissues. Both situations can result in the painful conditions of patellar chondromalacia and plica syndrome. Attempts to resist or correct this internal rotational torque by muscular effort can be created at several points along the lower extremity. As already mentioned, one mechanism is contraction of the tibialis posterior muscle of the leg. This attempts to counteract talar pronation by supporting the body of the talus against plantar flexion. A second mechanism is that of the popliteus muscle of the posterolateral aspect of the knee, attempting to internally rotate the leg. A third mechanism occurs at the buttocks, posterior to the hip joint. Here, the piriformis and external rotator muscles of the hip are well positioned to exert an external rotation effort on the lower extremity.

Figure 14.4 The angle formed between the line of the quadriceps musculature and the patellar tendon is termed the Q angle. Contraction of the quadriceps mechanism attempts to resolve the Q angle to 180 degrees. Therefore, the greater the Q angle, the larger the resultant lateral displacement vector force when quadriceps contraction occurs.

However, if these muscles, one or all are incapable of meeting the demand being made, the result will be breakdown, inflammatory reaction, and pain, with the consequences of initiating a vicious cycle of injury. This inability to meet the demand required might be due to a general lack of proper conditioning (relative overload), or it may be due to a truly excessive load being applied (absolute overload). In either event, injury will result.

At the knee, a breakdown of the popliteus tendon can present as posterolateral knee pain. The symptoms resulting from hip external rotator weakness will present as buttock pain. At the hip, these injuries can also affect adjacent but otherwise uninvolved tissues such as the sciatic nerve. The sciatic nerve lies in close proximity to and, in 15% of people, penetrates the external rotator muscles. Therefore, inflammation and stiffness of the external rotator muscles can create tethering of the sciatic nerve. This in turn can masquerade as an injury to the sciatic nerve or as a referral of symptoms of a more proximal injury (i.e., spinal trauma or intervertebral disk herniation).

It is hoped that this brief discourse on the interrelationships that exist within the lower extremity will prevent the examiner from approaching the lower extremity in a fragmentary fashion. It cannot be emphasized enough that the body, and lower extremity in particular, is a complex system of interdependent and interacting components. This concept is fundamental to the process of accurate diagnosis.

What is Gait?

Gait is the forward movement of the erect body, using the lower extremities for propulsion. Movement of any mass requires the expenditure of energy. The amount of energy required is a function of the amount of mass to be moved and the amount of displacement of that mass’ center of gravity along the X (anterior–posterior), Y (horizontal), and Z (vertical) axes from its point of origin. The body’s center of gravity is located in the midline, 1 cm anterior to S1 (first sacral segment) when the patient is erect with the feet placed a few inches apart and the arms at the side.

Chapter 14 Gait

What is Normal Gait?

Normal gait is the efficient forward movement of the body. Efficient means that energy expenditure is minimized. Any deviation from this minimum can be termed an abnormal gait pattern. There are varying degrees of abnormal. Normal gait therefore can be defined as the forward locomotion of the body during which the body’s center of gravity describes a sinusoidal curve of minimum amplitude in both the Y and Z axes (Figure 14.5). An increase in the displacement of the body’s center of gravity from this path requires increased energy expenditure, hence creating an increased metabolic demand. The result is decreased efficiency of locomotion and increased fatigue. This is why vaulting over a fused knee and leaning toward one side due to abductor weakness are patterns of abnormal gait. They are each characterized by increased displacement of the center of gravity. In vaulting, there is excessive vertical displacement of the center of gravity, whereas in the lateral list of the Trendelenburg gait, there is increased side-to-side translation of the body’s center of gravity.

Gait is a cyclical activity that requires repetitive positioning of the lower extremities. The gait cycle is divided into two phases: stance and swing (Figure 14.6). The stance phase is further subdivided into five discrete periods:

1Heel strike

2Foot flat

3Mid stance

4Heel off

5Toe off

The stance phase occupies 60% of the time during one cycle of normal gait. The remaining 40% of the gait cycle comprises the swing phase, which is divided into three periods:

1Initial swing (acceleration)

2Mid swing

3Terminal swing (deceleration)

The period when both feet are in contact with the ground is called double support. The step length is the distance between the left heel contact and the right heel contact. The stride length is the distance between one left heel strike and the next left heel strike.

There are six determinants of gait. These postural accommodations contribute to the efficiency of ambulation by reducing energy expenditure. The first five reduce the vertical displacement of the body. The sixth reduces lateral displacement of the body:

1Pelvic tiltaabout 5 degrees on the swing side

2Pelvic rotationaabout 8 degrees total on the swing side

3Knee flexionato about 20 degrees in early stance phase

4Plantar flexionato about 15 degrees in early stance phase

5Plantar flexionato about 20 degrees in late stance phase

6Narrow walking baseadue to normal knee valgus and foot placement.

During each cycle of gait, gravity is a downward force constantly acting at the body’s center of gravity. As such, it causes rotation to occur at each of the joints of the lower extremity. This rotational deformity is called a moment. A moment’s magnitude is a function of the size of the force acting and the perpendicular distance between the center of gravity and the axis about which the force of gravity is acting (the moment arm) (Figure 14.7). When the moment arm is the Z (vertical) axis, the resulting moments are termed varus, for rotation toward the midline, or valgus, for rotation away from the midline. When the moment results in the closing of a joint, it is termed a flexion moment. For example, at heel-strike, the body’s center of gravity is behind the axis of the knee. The moment arm acting at the knee is posterior to the knee joint’s center of rotation. The resultant moment of the body weight acting at the knee will close (reduce the angle) the knee joint, causing the knee to flex spontaneously. Therefore, the moment acting at the knee at heel-strike until midstance is a flexion moment (Figure 14.8).

b

G

Figure 14.7 The moment of varus (inward) rotation at the hip is the product of the force of gravity, G, acting at the body’s center of gravity, and the perpendicular distance, b, from the body’s center to the hip: moment of the hip = G × b.

Similarly, at heel-strike, the body’s center of gravity is anterior to the hip joint’s center of rotation. Therefore, the moment arm with which gravity acts at the hip during heel-strike will cause spontaneous closing (flexion) of the thigh on the torso. Hence, gravity acting on the hip at heel-strike creates a flexion moment.

When the moment acting on the joint creates an opening (increase) in joint angle, it is termed an extension moment. An example of an extension moment is the quadriceps contracting. The quadriceps pulling through the patellar tendon acts on a moment arm that is anterior to the axis of knee motion. It therefore opens (increases) the angle of the knee joint. Hence, the quadriceps extends the knee by virtue of the extension moment it creates at the knee when the muscle contracts.

The quadriceps extension moment serves to counteract the spontaneous flexion of the knee that occurs from heel-strike to midstance due to the posterior position of the body’s center of gravity relative to the axis of the knee.

By understanding the concept of moment, an analysis can be made for each joint throughout the gait cycle.

Chapter 14 Gait

Knee tends to flex

Quadriceps contract and resist knee flexion

Body weight

Left heel strike

Figure 14.8 At heel-strike, the body’s center of gravity is posterior to the axis of the knee joint. There will be a

spontaneous tendency for the knee to flex. This is called a flexion moment. This flexion moment is resisted by the active contraction of the knee extensors (quadriceps).

With such an analysis of the relative positions of the body’s center of gravity and the joint in question, it is theoretically possible to predict when a muscular structure must be active and where it should be positioned for optimal effect so as to maintain an equilibrium state of balance (erect posture) during gait. In other words, the muscles function to counteract the affect of gravity on the joints.

Conversely, an inability to maintain this equilibrium state can be analyzed so as to understand what structures are malfunctioning or malpositioned. Such an analysis is fundamental and crucial to the accurate diagnosis and treatment of gait abnormalities.

For example, limping due to hip disease can be analyzed into the gravitational moment acting to rotate the torso inwardly during unilateral stance and the counterbalancing valgus moment created by the abductor muscles (in particular, the gluteus medius). An example of a valgus moment is the action of the gluteus medius acting on the hip at unilateral midstance phase of gait. At this point in the gait cycle, the abductor muscle will contract. Its force vector

Hip abductors

Body weight

Figure 14.9 A cane held in the contralateral hand assists the hip abductor muscles in resisting the gravitational moment that pulls the body toward the unsupported side during swing phase.

will pull the pelvis in a valgus (outward) rotation. This will serve to counteract the varus (inward) moment created by the force of gravity. The abductor, however, has a shorter moment arm than does gravity with which to work. Therefore, the abductors must exert a proportionately greater force than that of gravity in order to balance the body across the hip joint. In fact, since the abductor moment arm (a) is about one-half that of the body’s (b), the abductor force (A) must be twice that of the weight of the body (B)athe action of gravity pulling at the body’s center of gravity. This can be expressed as an equilibrium state equation: A × a

= B × b, knowing a = b, then A = 2B. With such an analysis of the hip, it is easy to predict the usefulness of a cane held in the opposite hand as a means to assist weak abductor musculature. The cane will prevent the inward rotation of the torso toward the unsupported side caused by gravity and insufficiently resisted by weak abductor muscles (Figure 14.9). Similarly, analysis of the knee will explain how bracing the knee in extension is an effective means of protecting a polio victim with quadriceps paralysis from sudden spontaneous knee flexion and falling during gait.

The Examination of Abnormal Gait

As stated above, the evaluation of abnormal gait requires a working knowledge of normal biomechanics. Abnormalities occur as a result of pain, weakness, abnormal range of motion, and leg length discrepancy. These factors can occur separately or together. They are closely interrelated. For example, weakness of a muscle group can result in a painful joint, which would then lose normal range of motion. When isolated, however, pain, weakness, abnormal range of motion, and leg length discrepancy within a particular anatomical region result in a characteristic gait abnormality. Some of these abnormalities were referred to in prior chapters.

Gait disorders due to central nervous system disease or injury, such as spastic, ataxic, or parkinsonian gait, are not described here, as they are beyond the scope of this text.

The key to observing abnormal gait is the ability to recognize symmetry of movement. You should observe the patient walking for some distance. Sometimes it is necessary to watch the patient walk down a long hallway or outdoors. Subtle abnormalities will not be evident inside the examining room. A patient will walk differently when he or she is “performing” for you. If it is possible, try to observe the patient when he or she is not aware of being watched.

The foot and ankle, knee, and hip should be observed separately for fluidity and degree of motion. The examples that follow are meant to illustrate how pain, weakness, abnormal range of motion, and leg length discrepancy affect the normal symmetry of motion that occurs at the foot and ankle, knee, and hip (Table 14.1).

Foot and Ankle

Antalgic Gait

The patient with pain in the foot or ankle will make every effort to avoid weight bearing on the painful part. For example, if the first metatarsophalangeal joint is painful due to gout, the patient will not want to extend that joint. This results in a flat-footed push-off. The weight is maintained posteriorly on the foot. The patient will also spend less time in the stance phase on the painful foot, causing an asymmetrical cadence (Figure 14.10).

Abnormal range of motion and leg length discrepancy

Compensatory movement in other joints to allow for weight-bearing,limb clearance, or relocation of the center of gravity over the weight bearing limb.

Weakness

Weakness of the dorsiflexors of the foot due to peroneal nerve injury, for example, will result in a drop foot or steppage gait. Inability to dorsiflex the foot during swing-through will cause the toes to contact the ground. To avoid this from happening, the patient will flex the hip and knee in an exaggerated fashion as if he or she were trying to climb a stair so that the foot will clear the ground during swing-through (Figure 14.11). This is called a steppage gait.

Eccentric dorsiflexion of the foot also occurs as the body weight is transferred from the heel to the forefoot following heel-strike. Weakness of the foot dorsiflexors results in a slapping of the foot against the ground following heel strike, known as foot slap (Figure 14.12).

Abnormal Range of Motion

If the ankle is unable to dorsiflex, as in an equinus deformity (Figure 14.13), the patient lands with each step on the metatarsal heads. This is known as

Figure 14.10 An antalgic gait due to pain in the great toe or foot will result in a shortened stance phase.

Tibialis anterior

Figure 14.11 Weakness of dorsiflexion results in a steppage gait with increased hip and knee flexion to allow for clearance of the toe during swing-through.

Figure 14.12 After heel-strike, with weakness of foot dorsiflexion, the patient’s forefoot slaps against the ground. This is called foot slap.

Figure 14.14 With a talipes equinus deformity of the foot, the patient contacts the ground with the ball of the foot instead of the heel. This is called primary toe-strike.

Figure 14.13 A talipes equinus deformity of the foot.

primary toe-strike (Figure 14.14). Due to the primary toe-strike, the line of force is far in front of the knee and this causes a hyperextension moment at the knee. Therefore, the patient may develop genu recurvatum as a result of an equinus deformity. As in the case of foot drop, the patient will again have difficulty preventing the toes from hitting the ground during swing phase. The patient will therefore have to elevate the foot in the air by either increasing knee and hip flexion as in a steppage gait, circumducting the leg at the hip (Figure 14.15), or hiking the extremity up from the hip

(Figure 14.16). These maneuvers effectively shorten the leg and allow for toe clearance during swing-through.

Knee

Antalgic Gait

The patient with a painful knee will walk with less weight on the painful side. Less time will also be spent on that side. The patient will attempt to maintain the knee in flexion if there is an effusion. If the knee is kept in extension, the patient will have to circumduct at the

Figure 14.15 An equinus deformity of the foot will result in relative lengthening of the extremity and the patient must circumduct the hip in order to clear the ground.

Figure 14.16 The patient may also clear the ground with the relatively lengthened extremity due to an equinus deformity by hip hiking.

hip or hike the lower extremity upward from the hip in order to clear the ground during swing-through. Heel-strike is painful and will be avoided.

Weakness

Quadriceps weakness is common in patients with poliomyelitis. The gait abnormality that results is hyperextension of the knee following heel-strike. The patient has to try to maintain the weight in front of the knee to create an extension moment. This is effected by throwing the trunk forward following heel strike. The patient may also attempt to extend the knee by pushing the thigh backward following heel contact (Figure 14.17). Weakness of the quadriceps frequently results in overstretching of the posterior capsule of the knee joint and this causes genu recurvatum.

Abnormal Range of Motion

Loss of full knee extension will result in a functionally shorter extremity. The patient will have to elevate

the body on the normal side as that leg tries to swing through while he or she supports the weight on the abnormal side. This can be accomplished by hip hiking or circumducting the hip on the good side during swing-through. To allow for weight bearing on the affected side, the patient will walk on the ball of the foot (primary toe-strike).

Hip

Antalgic Gait

The patient with the painful hip due to osteoarthritis, for example, will make every effort to reduce the amount of time spent weight bearing on that side. The trunk is thrown laterally over the hip during weight bearing. This is done in an effort to reduce the compressive force of the abductor muscles of the hip during weight bearing. This is known as a compensated Trendelenburg or lurch gait (Figure 14.18). The hip is maintained in a relaxed position of external rotation during swing phase. Heel-strike is avoided.

Figure 14.17 Weakness of the quadriceps may be compensated for by the patient pushing the thigh backward following heel strike when quadriceps function is necessary.

Figure 14.18 The compensated Trendelenburg gait is characterized by the trunk deviating over the hip during stance phase to make up for weakness of hip abduction. This gait pattern may also be noted in patients with a painful hip, in which case the stance phase duration will be markedly reduced.

Weakness

Weakness of the hip abductors, seen frequently in patients with poliomyelitis, results in a Trendelenburg gait. This is characterized by abduction of the hip in stance phase. It appears as if the patient is bending the trunk to the side, away from the weak hip during weight bearing (Figure 14.19). Some patients may compensate for this by flexing their trunk over the weight-bearing hip. This is called a compensated Trendelenburg gait. A compensated Trendelenburg gait results from weakness of hip abduction or a painful hip. You can differentiate the cause of this gait pattern by observing the duration of the stance phase on the abnormal leg. With a painful gait, the stance duration is reduced. Weakness has a lesser effect on stance duration.

Weakness of the hip extensors, seen frequently in myopathies, results in the trunk being thrown posteriorly at heel strike, when the hip extensors are normally most active.

Abnormal Range of Motion

Loss of hip extension that occurs due to a hip flexion contracture, for example, will cause a functional shortening of the patient’s leg. An increase in the lumbar lordosis will develop so that upright posture of the trunk can be maintained. The patient may walk with the foot plantar flexed on the shortened side to increase the functional length of the leg. Increased knee flexion will occur on the contracted side during late stance phase, when the hip is normally in extension.

Leg Length Discrepancy

Leg length discrepancy may be absolute or relative. Absolute leg length discrepancy results from a lengthening or shortening of the extremity due to bony