American Academy of Orthotists & Prosthetists

Clinical Assessment of Human Gait

Deanna J. Fish, CPO
Jean-Paul Nielsen, CP

ABSTRACT

The mechanics of human gait involve synchronization of the skeletal, neurological and muscular systems of the human body. This article will enhance the gait assessment abilities and processes of the novice clinician by providing a brief overview of normal gait followed by identification of pathological and pathomechanical gait patterns. Also presented is a systematic approach to clinical gait assessment that emphasizes the need for the development of clinically cost- and time-effective tools to document and quantify data in the assessment of human gait.

Introduction

The complexity of the interactions of the various components of human gait has been researched and documented for many years. Modern technological advances such as force platforms, electromyographic data, high-speed film and computerized gait analysis laboratories have allowed new insights into human bipedal ambulation. While these advances have proven to be invaluable in explaining "normal" gait, and to some extent "abnormal" gait, the experienced clinician continues to perform functional gait assessment in the absence of most technological assistance.

As a result, one has to rely on a trained clinical eye to capture all phases of the gait cycle in a short period of time for functional analysis. This requires a thorough understanding of normal gait and a systematic approach to the evaluation of abnormal ambulatory patterns.

Normal Gait Patterns

The term "gait" is used to describe a particular manner or style of walking, and the term "normal gait" is used to present those parameters that have been generalized across sex, age, genetic predisposition and anthropometric variables.

The eight subphases of "normal" gait have been well-described by Perry and include: initial contact (IC), loading response (LR), midstance (MSt), terminal stance (TSt), preswing (PS), initial swing (ISw), midswing (MSw) and terminal swing (TSw)(1,2). However, without technological assistance, these eight subphases of gait cannot be reliably distinguished. Four divisions for functional gait assessment procedures are necessary to accumulate relevant information in the analysis of normal gait. These include:

• Weight Acceptance (initial contact and loading response)

• Stance (midstance and terminal stance)

• Forward Progression (terminal stance and preswing)

• Swing (initial swing, midswing and terminal swing)

A gait cycle is defined as the time between two successive occurrences, for example, from a right weight accep tance period to the next right weight acceptance period (3). It has been wellestablished that dynamic ambulation involves a stance phase of 60 percent of the entire cycle and a swing phase of 40 percent (see Figure 1 ). Two additional periods of double-limb support exist when both the right and left lower extremities contact the ground in opposite synchronization.

Seventy percent of the total body mass is located in the head-arms-trunk (HAT) segment (2). This mass progresses in a hypothetical line of progression (LOP) and is balanced during ambulation on the lower extremities, which form the remaining 30 percent of total body mass (4). The body's ability to effectively balance this mass in both static and dynamic situations is essential to the functional goals of bipedal ambulation.

These goals include providing a stable base of support in stance, allowing forward progression of the body mass over the distal limb segments, maintaining minimum energy expenditure, and employing appropriate mechanisms for shock absorption and dissipation of forces.

Figure 2 is a summary of the major sagittal plane joint motions and functions during a complete gait cycle. All joint angulations are approximations based upon a consensus of current literature, and the reader should refer to these reference sources for detailed analysis of normal gait patterns. It should be understood that the timing of muscle actions to produce specific joint motions is critical for a stable, efficient bipedal mode of ambulation. Even minor disturbances of the neurological control mechanisms, motor input and structural skeletal alignment can have a significant effect on dynamic stability and on functional and energy-efficient gait.

Pathological Gait

Pathological gait describes altered gait patterns that have been affected by deformity (usually in the form of contractures), muscle weakness, impaired motor control (including sensory loss and spasticity) and pain (3). Any alteration affecting one or more motion or timing pattern can create a pathological gait pattern. Even minor alterations can increase energy expenditure and progress to pathomechanical involvements.

Deviations to normal gait patterns can be observed during both swing and stance phases and require systematic evaluation for assessment of functional compensations and/or neuromuscular-skeletal factors. Functional compensations are voluntary posturings that attempt to substitute for specific motor weaknesses and joint instabilities. It is important to identify functional compensations from imposed mechanisms for appropriate orthotic design and therapeutic considerations.

Swing phase characteristics of pathological gait are summarized in Figure 3 , Figure 4 , Figure 5 , and Figure 6 , with identification of the most commonly recognized functional compensations and neuromuscular-skeletal factors. Beginning proximally with pelvis and trunk involvement, observations should be made of sagittal, coronal and transverse plane alignments. Greater disturbances or displacements of this proximal mass (HAT) create increased demands on the lower-limb segments and alignments to maintain dynamic balance and stability. They also significantly increase energy costs. Functional compensations are evidenced by anterior, posterior and lateral trunk leans. Pelvic involvement is primarily due to neuromuscular factors (both tone-induced patterns or motor weaknesses) but can also result from skeletal anomalies and distal instabilities.

Pathological hip joint involvements are triplanar and are both compensatory and physical in nature. As with all joints, skeletal anomalies can affect both dynamic motion patterns as well as stance phase stability, and thorough assessment and identification of these factors must be made (see Figure 4 ).

Sagittal plane deviations of the knee joint include excessive flexion and extension alignments during swing phase. Excessive flexion may either assist in ground clearance due to related factors or may be the result of contracture or flexor synergy (see Figure 5 ).

The ankle joint rarely exhibits functional compensations during swing phase as its alignment is critical for ground clearance (see Figure 6 ). Excessive plantarflexion makes ground clearance difficult and induces more proximal compensations while excessive dorsiflexion is rare and is most often an attempt to compensate when a painful joint decreases hip or knee flexion.

Pathological gait deviations in stance phase may be the result of functional compensations or neuromuscular-skeletal factors. In conjunction with swing phase deviations, observations can identify "excessive vertical displacement of the COM, poor use of body momentum, marked inefficiencies in the transformations between kinetic and potential energies, and increased energy requirements" (4).

Beginning distally with the foot and ankle, stance phase deviations can be observed from weight acceptance through forward progression and their proximal joint and alignment implications properly identified. Functional compensations are primarily found with leg length discrepancies and pain-avoidance patterns. Proximal joint limitations might also impose compensatory alignments and compensatory mechanisms such as vaulting for contralateral ground clearance during swing (see Figure 7 ). Neuromuscular and skeletal factors are numerous and individual evaluation and assessment is critical. Tone-induced posturings and contracture formation are common in pathological gait, and specific muscle weaknesses can also engender imbalances and therefore deviations.

Foot and ankle posturings will have a direct effect on knee joint alignment during weightbearing. Excessive posterior and anterior moments at the knee will be created by excessive plantarflexion and dorsiflexion at the ankle, respectively (see Figure 8 ).

Hip joint stability during stance phase is critical as it is the direct link between the lower extremity and the heavy HAT section. Even minor weaknesses evidenced at the hip can create great displacement of the proximal body mass and significantly alter weightbearing and ground reaction lines while increasing energy costs (see Figure 9 ). Functional compensations for ankle and knee alignments can be noted as well as neuromuscular factors such as spasticity and specific weaknesses.

Maintenance of the proximal body mass segment is directly related to hip joint alignment as well as more distal joint alignments and is necessary for dynamic stability (see Figure 10 ). Gross displacements will increase energy costs but may also serve as functional compensations for other deficiencies such as muscle weaknesses, distal contractures, leg length discrepancies or painful joints.

Pathological gait patterns may significantly alter the magnitude of the lever arm forces imposed on the lower extremities. Unaddressed, these forces may abnormally stress ligamentous structures with resulting laxities at the midtarsal, subtalar and/or knee joints. When unable to return to neutral joint angulation alignment under static weightbearing, these joint posturings may signal the genesis of pathomechanical gait.

Pathomechanical Gait

The ERD-IRD Model in Pathomechanical Gait

Pathomechanics is a branch of physical science that deals with static and dynamic forces and their abnormal effect on a human body affected by neurological, muscular and skeletal disorders. As this relates to clinical gait assessment, a potential lower extremity pathomechanical deformity is identified when a lever arm has changed from the "normal" profile of the lower limbs. Such a change is usually caused by neuromuscular, velocity or balance factors and results in excessive vertical or horizontal displacement of the COM. An actual lower-extremity pathomechanical deformity is identified when the skeletal system is:

• unable to return to neutral joint angulation alignment under full static weightbearing at one or more of the following joints: midtarsal, subtalar and knee joints. This misalignment usually results in excessive internal or external transverse plane rotation of the biomechanical axis of the talocrural joint when the knee axis is aligned perpendicular to the line of progression.

• Altered structurally from surgery, which results in actual skeletal lever arm changes.

The evaluation process used in identifying potential and actual pathomechanical deformities that affect gait should be time- and cost-effective, logical and relate mechanically to the skeletal structure of the human body in all three planes of motion. With the notable exception of lever-arm alterations in the structure of the skeleton (skeletal pathomechanics), most lower-extremity deformities are the result of ex exessive internal or external transverse plane rotation at the foot and ankle and at the hip joint.

In human bipedal ambulation the body mass advances in a theoretical line of progression through a complex sequential process of muscle- and gravity-powered joint rotations. The line of progression is defined as the hypothetical path of the COM simplified by integrating the different movements of all three perpendicular planes of reference into a single compound unit (5).

The External Rotary Pathway

The external rotary pathway (ERD) is the biomechanical skeletal realignment of a limb being maximally torqued externally in the transverse plane from proximal to distal by muscle power under full weightbearing with the body in the anatomical position. Reacting to this external moment, the foot will simulate a supinated position, and certain observed and inferred skeletal changes will occur from distal to proximal (see Figure 11 ).

The Internal Rotary Pathway

The internal rotary pathway (IRP) is the biomechanical skeletal realignment of a limb being maximally torqued internally in the transverse plane from proximal to distal by muscle power under full weightbearing with the body in the anatomical position. Reacting to this internal moment, the foot will assume a pronated position, and certain observed and inferred skeletal changes will occur from distal to proximal (see Figure 12 ).

The ERD-IRD Pathomechanical Models

Alteration of functional lever arms in the lower extremities from factors imposed by variations in the neuromuscular system often results in abnormally magnified forces. When these forces place constant and unrelieved tension on the ligamentous structures of the midtarsal, subtalar and knee joints, especially under weightbearing and with the body mass in motion, ligamentous laxity will often result and the ensuing pathomechanical deformity (ligamentous pathomechanics) will progress along one of the biomechanical rotary pathways. When clinically identified, such a deformity is classified as verse plane but which subsequently either an ERD or as an IRD whose primary plane involvement is the transverse plane but subsequently also involves deviations in both the coronal and sagital planes.

In ligamentous pathomechanics, very few deformities' primary plane involvement is not the transverse plane. These are called non-rotary deformities (NRD). They originate in the knee joint (e.g., osteoarthritis) and develop opposite angular compensations at the foot and ankle (see Figure 13 ).

Other pathomechanical exceptions to the ERD-IRD model include foot deformities distal to the midtarsal joint such as ray deformities or hallux valgus. It should be noted that one of the mechanical causes of hallux valgus is an IRD.

An ERD is a pathomechanical lower-extremity skeletal joint angulation deformity in which the tibia-fibula structural unit rotates externally so that each bone and joint follows the established biomechanical external rotary pathway. To achieve plantigrade position at midstance, there is some compensatory forefoot pronation. When there is 10 or more degrees of calcaneal varus angulation relative to the horizontal of the floor, full forefoot compensatory pronation to achieve a plantigrade position is not possible because of the skeletal limitation of the foot (see Figure 14 ). An IRD is a pathomechanical lower-extremity skeletal joint angulation deformity in which the tibia-fibula structural unit rotates internally. The foot almost always achieves plantigrade position as there is full forefoot compensatory supination. Usually ligamentous laxity occurs at the midtarsal and subtalar joints and frequently also at the knee joint. With a compromised anterior foot lever arm there is usually a plantarflexion contracture at the talocrural joint with pathomechanical dorsiflexion occurring at the midtarsal joint in stance phase. An IRD gait pattern is almost always a stance phase deformity (see Figure 15 ).

Pathomechanical Knee Involvement

In normal gait, transverse plane internal and external torque is transferred from the talus directly to the tibia and fibula and thus to the knee joint. For example, supination of the foot and ankle under weightbearing will externally rotate the talus transferring this torque proximally to the knee joint with the opposite being true for pronation and internal rotation of the talus. This has been previously described by Rose, Inman and Sarrafian (6,7)

As an ERD progresses, the hypothetical center of the ankle joint (talus) is positioned posteriorly and laterally from neutral. In addition, the talus has externally rotated relative to the forefoot and to the LOP. This external torque is transferred proximally to the knee joint and, while the ligamentous structures of the knee are intact, to the hip joint. Due to this torque in the transverse plane and to skeletal alignment, the knee is subjected to hyperextension and varum forces during single-limb stance. The possibility of a genu recurvatum is created by the sustained rigidity of the foot and ankle structures which, combined with the body mass in motion, can result in ligamentous laxity at the knee joint.

An IRD predisposes the knee joint to internal rotary, flexion and valgum forces. When accompanied by quadriceps weakness, the knee joint assumes a position of hyperextension to prevent joint collapse when the body mass is static and frequently when it is dynamic. An IRD recurvatum is defined by the ensuing knee ligamentous laxities and will usually not progress significantly due to the loss of foot and ankle rigidity from ligamentous laxity at the midtarsal joint. Such a recurvatum will develop perpendicular to the joint axis (determined by the talus which is excessively internally rotated) and proceed from anterior-medial to posterior-lateral.

A pathological gait can thus deteriorate into a pathomechanical gait when ligamentous laxities result from an IRD, ERD, NRD or skeletal pathomechanical deformity due to a progressively changing lever arm profile.

Evaluation of Pathomechanical Deformities

Clinical assessment of pathomechanical deformities requires a systematic approach. Initiating treatment without identifying the primary and secondary involvements can lead to ineffective o even damaging programs for the patient.

Information necessary for clinical gait assessment is patient history, muscle/neurological evaluation, static alignment, angulation measurements dynamic alignment, pathological/pathomechanical conclusions and orthotic recommendation.

Patient History

Considerations should be made regarding the age, height, weight, diagnosis. prognosis, current ambulation limitations, date of onset, chief complaints, realistic goals, current and past medications, "normal" ambulation ideals, assistive devices, edematous conditions, activity level and other medical problems. This information should be specific to each patient so an appropriate and representative "ideal" patient model can be formed.

Muscle/Neurological Evaluation

A muscle/neurological evaluation is best provided by a physical therapist or other trained medical professional. This information will help identify generalized motor deficits, specific weaknesses/strengths, tone pattern involvements, proprioceptive deficits, range-of-motion limitations and coordination limitations.

Static Alignment

During static alignment, assessment is made of the skeletal integrity and alignments of the entire body posturing. The patient is asked to stand in a relaxed, comfortable position with equal weight through both lower extremities. The patient should face straight ahead with shoulders and pelvis squared. Assessment of static alignment should examine the skeletal alignments of the foot and ankle complex, knee and hip as well as the posturing of the pelvis and trunk. IRD, ERD or NRD classification can be made at this time.

Angulation Measurement

These measurements can be gathered from the patient directly or assessed from photographs. Measurements must be acquired in the upright, weightbearing position and relate to only constant factor available- gravity. This vertical reference line relates each specific segment of the human body in space independent of proximal and distal components and is used to document correction or monitor progression of a structural deformity.

Standing angulation measurements should include calcaneal angulation in the coronal plane, talocrural attitude in the sagittal plane, knee attitude in the coronal and sagittal planes, hip attitude in the coronal and sagittal planes, sacral attitude in the sagital plane, and pelvic attitude in the coronal plane.

Talocrural transverse plane rotation is also important in establishing the degree of internal or external torque generated and dissipated throughout the extremity.

Dynamic Alignment

Asking the patient to ambulate, in the safety of parallel bars if necessary, the clinician observes the dynamic relationship between all body parts. Clinical gait assessment is divided into two major component parts: stance phase and swing phase.

It is important to establish and verify the inter-relationship of all body segments during both swing and stance.

Pathological/Pathomechanical Conclusions

Pathological gait patterns, such as specific quadriceps weakness, can predispose a patient to the development of pathomechanical deformities. Such deformities could progress as a result of the typical compensatory posturing of hip external rotation and sustained knee extension. This compensatory mechanism is unconsciously aligned to rotate the knee axis externally relative to the LOP while manipulating the COM anteriorly to the knee joint during stance to provide stability against collapse.

In the case of an identified skeletal pathomechanical deformity, ligamentous laxities can often be expected. In the pediatric population, ligamentous laxities might lead to skeletal malformation if these structures develop and ossify during growth in a misaligned posturing. Often, neuromuscular deficits alter skeletal alignment and create abnormally high forces to ligamentous structures primarily at the midtarsal, subtalar and knee joints. It is important to identify and remove potentially damaging forces before they create ligamentous laxities and deformation. A key factor in this process is predictability given skeletal structures, possible joint alignments and planes of motion.

Orthotic Design and Recommendation

The end result of the clinical gait assessment procedure for the orthotist is the determination of the orthotic design and recommendation. Orthotic design takes the form of three-point force systems specific to the joint angulation alignments, the planes of deviation and the necessary support due to motor deficits.

Three-point force systems may be either structural or ground reaction in nature. Structural three-point force systems provide joint stability by physically bridging the joint in question. All three-point force systems have in common the following elements:

• Point No. 1 is distal to the joint in question and on the concave side of the deformity

• Point No. 2 is at the joint in question and on the convex side of the deformity

• Point No. 3 is proximal to the joint in question and on the concave side of the deformity.

Three-point force systems incorporating ground reaction principles follow the same general format of force application but do not structurally ridge the joint in question. Ground reaction orthotics has been defined as "a branch of orthotics in which an orthosis applies a stabilizing force to a proximal joint without structurally bridging that joint, utilizing both mass in motion and floor reaction as two of the three forces in a three-point force system" (8). It is in this manner that a foot orthosis can stabilize the subtalar joint in the coronal plane without crossing the subtalar joint, and an ankle-foot orthosis can effectively address a knee instability in the sagittal plane without structurally bridging the knee joint.

With thorough assessment of the structural deformation and motor deficits in mind, an orthotic design will incorporate the necessary three-point force systems to effectively counteract the deforming forces and prevent progression. Most orthotic designs are a combination of structural and ground reaction three-point force systems used in series.

Deanna J. Fish, CPO, is marketing director at Oregon Orthotic System Inc., 2280 Three Lakes Road, S.E., Albany, OR 97321.

Jean-Paul Nielsen, CP, is CEO, president and clinical consultant at Oregon Orthotic System Inc., 2280 Three Lakes Road, S.E., Albany, OR 97321.

References:

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8. Adapted from Nielsen JP. Fish Di. Unpublished course material for OOS-l Basic Seminar in Pathomechanical Deformities. Lower Extremity Derotational Orthotics: ERD - IRD Model 1991.