Seated Impact

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June 2005

By Caroline Portoghese, OTR/L

Tight hamstrings can cause significant challenges for patients

Caroline Portoghese

Tight hamstrings can have a profound impact on seating. They are, however, a commonly overlooked issue that even experienced medical personnel miss. Because the hamstrings pull over two joints—the hip and the knee—the biomechanics are more complex. This effect has an impact on seated postural alignment, skin integrity, and function. The role in wheelchair management of tight hamstrings is to accommodate, not lengthen, the hamstrings.

The biomechanics involve both the hip joints and the knee joints. The hamstrings are made up of the three posterior thigh muscles: the semitendinosus, the semimembranosus, and the long head of the biceps femoris. The proximal attachment of these muscles is the "sitting bone," or ischial tuberosity—the large, bony prominence near the gluteal fold. They attach distally, just below the knee, at the medial and posterior surface of the superior part of the tibia, and the lateral side of the head of the fibula. The primary actions are hip extension and rotation, and knee flexion. When the thigh and knee are flexed, such as when seated, they extend the trunk. Hamstrings are at their longest stretch when the pelvis is in anterior pelvic tilt, the hip is flexed, and the knee is extended.

TIGHT EFFECTS
Clinically, tight hamstrings can have a profound effect on seated postural alignment. Posterior pelvic tilt is a primary effect, with resultant kyphotic thoracic spine, and stress on the cervical spine—either hyperextended or flexed. Feet may migrate posteriorly off the footrests, and the hips may abduct from decreased distal thigh support. Frequent repositioning is often required because of almost constant sliding down in the seat. If hamstrings are unequally tight, the pelvis will rotate away from the tighter hamstring. For example, if the right hamstring is tighter, the pelvis will rotate toward the left. Early unsuccessful attempts to remedy this problem commonly involve a posterior calf support, a posteriorly tilted wedge, or a pommel. The calf strap is often placed to keep the feet forward on the footplates of the wheelchair, which actually worsens the postural effects of the tight hamstrings because this increases their pull. Wedges are often added to try to reduce sliding, but they actually make the problem worse because they flex the hips even further past 90°, which is already not tolerated. A pommel, which has minimal effectiveness, places the individual at risk for pain and injury in the pelvic area, as they slide involuntarily into it.

SKIN INTEGRITY
Skin breakdown can occur as a result of ineffective management of tight hamstrings. The main risk of skin injury associated with tight hamstrings is attributed to pressure and shear forces on bony prominences. Pressure is a force that is perpendicular to the skin surface. It damages the skin by cutting off blood flow, causing cell damage because of the lack of oxygen or nutrients, or because there is not sufficient blood flow to carry away cellular waste materials. This may start by leaving discolored circular marks on the skin, corresponding to the underlying bony prominence. These sores can open and become serious if they are not addressed.

The effects of pressure are often more easily observed than shear, and they can be measured by pressure mapping. Pressure can be increased on the coccyx when the pelvis is in posterior pelvic tilt. The ischial tuberosities are also at risk if the individual slides up onto the proximal thigh support of a contoured cushion. Feet are also at risk for injury. The posterior aspect of the heels press back and impinge on wheelchair components, increasing the risk of tissue damage.

Friction-shearing forces are difficult to measure, but they can be significant as an individual slides down repeatedly in their chair. Shear forces are forces parallel to the skin surface that tear the skin, sometimes into visible tearlines. Shear forces are present and can cause damage even if the individual does not actually move but is in a shear-prone position. The primary areas of skin-integrity concern are the ischial tuberosities and the coccyx. The bony prominences of the thoracic spine can also be at risk with the combination of a kyphotic posture and the tendency to slide. Acute injury, such as sliding down and out of the wheelchair, or foot entanglement in the casters, is of additional concern with the seated posture associated with tight hamstrings.

FUNCTION

Patient sitting in posterior pelvic tilt

Patient with tight hamstrings sitting in posterior pelvic tilt in order to relieve hamstrings.

Function can be impaired if the hamstrings are not well managed in the seated position. Commonly, the individual has difficulty raising their head, so they spend much of their seated time facing their own lap. This posture contributes to poor eye contact, and commonly affects socialization and attention; this is of particular concern when patients have symptoms of depression or cognitive impairments. Upper-extremity function is often severely compromised because people attempt to hold themselves upright in the wheelchair. When an attempt to use the arms functionally is made, the individual may collapse further into kyphotic collapse, or slide down further into the wheelchair. This posture commonly interferes with the ability to drive or propel the wheelchair because access to the wheels, joystick, or alternate drive controls, such as a head array, is lost when an appropriate posture is not supported. Fatigue is also a potential concern because of the overuse of the upper extremities while attempting to maintain postural alignment.

HAMSTRING MANAGEMENT
One of the most effective ways to check for tight hamstrings is a mat evaluation. Place the person on their back with their pelvis in neutral tilt. Hold the pelvis stable, and slowly flex the hip and knee upward. When you feel the pelvis start to move into posterior pelvic tilt, you have found the end range. Now visualize where the wheelchair and seating components need to be to support this individual

Accommodation is the role of the wheelchair and seating system in the management of tight hamstrings. This needs to be done by either posteriorly recessing the footrest, allowing the knees to flex; opening up the hip angle; or using both in combination. Either way equally accommodates the shortened muscles, but they have different implications.

If the footrests are recessed, care needs to be taken to see that the feet do not impinge on the wheelchair components, often the casters of either a power or manual wheelchair. Standard wheelchair footrests are at 70°, so changing the footrest hangers to 80° or 90° may be sufficient for the more minimally tight hamstrings. If seat height is not critical, sometimes raising the individual within the frame of the wheelchair will give adequate foot clearance above the casters. It is important to see that the other components of the wheelchair can accommodate this change, such as the armrests, laptray, backrest, and headrest. One must also check to see that a raised height does not interfere with power-wheelchair functions—such as recline—or impair safe propulsion of a manual wheelchair.

The same client with back angle opened up and custom cushion allowing for stabilization of the pelvis and lowering of the distal thighs as well as moving the footplates back to 90° to allow for hamstring tightness.

Environmental access must also be considered. Will a change in height affect transfers or environmental access, such as entrance into a personal van, or movement under a desk/table? Sometimes, an environmental modification, such as raising the height of a desk/table, offers increased options with wheelchair seating. If the feet continue to contact the casters, consider the size and location of the casters. Different wheelchair brands, and different options, are available to address this concern. If the feet can be recessed, the angle of the footrests must also be addressed. The toes will be lower than the heels if the knees are flexed. Angle-adjustable footrests, or wedges on footrests, may be necessary. The front edge of the cushion must also be considered. Ideally, it will provide full distal thigh support, but the anterior edge will need to be angled posteriorly toward the lowest part of the cushion. This means the cushion will be longer on the top, and angle back and be shorter on the bottom, to accommodate the posterior foot position, so the calf will not impinge on the lower anterior edge of the seat cushion.

Reclining the back angle, while maintaining a level, or slightly posteriorly tilted, seated position, is another way to accommodate tight hamstrings. A reclined back, in combination with a posteriorly tilted seat, allows gravity to facilitate postural alignment. This position can limit transfer options if the seating system cannot tilt forward. This can interfere with functional gaze, by positioning the person so they have only a good view of the ceiling instead of other people and activities. It may be difficult to maintain for people with a poor swallow, or difficulty breathing. Opening the hip angle requires either reclining the back or tilting down the front edge of the seat. Tilting the front edge of the seat creates a difficult-to-maintain, high-shear situation. It can sometimes be tolerated for short periods of time for a functional task, such as a transfer or a short meal, in combination with the use of a tilt-in-space feature. The tilt allows the person to spend only short periods of time on this "slide," and then tilt back to a more easily maintained position.

The combination of components used to accommodate tight hamstrings for each individual is determined by weighing all of the positive and negative factors of each possibility, attempting to minimize the drawbacks associated with each factor, and maximizing the overall benefit. Once the best solutions are determined for the individual, two factors will improve success: proper placement in the wheelchair, and an appropriately placed hip belt.

No seating system will work well if a person is placed in it "however they land." It is like expecting a high-performance pair of running shoes to work when untied and placed on the wrong feet. The person needs to sit with the hips all the way back, centered, and leveled in the seating system. Patient and caregiver training is often necessary to achieve this goal. To maintain this position, a hip belt, fastened below the anterior hip, the ASIS (anterior superior iliac spine), at approximately a 45° angle, and fastened snugly, can be very effective. It is not uncommon to have professional resistance to a hip belt, because of the worthy concern of restraint reduction. Although it can have a secondary effect of keeping a person in the wheelchair, the primary effect, in this case, is to maintain proper seated position to maximize physical, cognitive, and emotional health, as well as to maximize function. The purpose is orthopedic support, not restraint.

Without a comprehensive approach to seating and positioning, the individual may be even more restrained by having to spend a significantly greater time in bed. This delicate topic needs to be frequently reassessed and carefully documented.

Hamstring stretching is not a realistic expectation of a wheelchair or seating system. When tight hamstrings are identified as contributing to problems with the seated position, they must be accommodated to manage postural alignment. If the shortening of hamstrings is to be slowed or reversed, it should be addressed by other methods. Other areas to be considered would include bed positioning, use of splints and range of motion, therapeutic modalities, medical management of spasticity, and surgical intervention.

Caroline Portoghese, OTR/L, has been an occupational therapist for 10 years. Her primary focus and passion has been in seating and positioning, and its impact on overall function, health, and patient satisfaction. She currently works at Fairview Rehabilitation Services in the Seating and Wheeled Mobility Clinic, Minneapolis.

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