UNEQUAL LEG LENGTH
The leg is too long (usually)
"After the operation of my left hip the leg has been to long. My PT told me that doctors have difficulty to achieve equally long legs after the total hip surgery. " (Patient, 2001)
"Over-lengthening of up to 1 cm can be justified because ....it permits active rehabilitation ...and patients very soon become adjusted to 1 cm of over-lengthening. Since men nowadays wear raised shoes for cosmetics, slight lengthening is less important."
Sir John Charnley, 1979, Founding Father of the total hip surgery
Facts first:
In patients with equally long legs before the surgery, the operated leg is more often longer after the total hip replacement:
Leg length difference Percent of all patients Leg length difference within 10 mm 72 %
Operated leg longer > 10 mm 22 % Operated leg shorter > 10 mm 8 % (White 2002)
Even patients with equally long legs after a total hip replacement may perceive their operated leg as longer immediately after the operation. This is called apparent leg length difference.
Usually, this perception disappears successively with training and stretching of the musculature within three months.
If the limb on the operated on side became really longer after the total hip replacement, the patients complain more often about this situation.
If the operated on leg became shorter after the total hip operation this difference is less disturbing to the patients. As you see from the Table this is happening rather seldom.
Inequality in leg length greater than 1,5 cm has been shown to produce low back pain and abnormal gait with higher energy consumption and early fatigue.
Desirable and undesirable leg lengthening after total hip replacement
Some patients have had the operated on leg the leg shorter already before the surgery because of previous deformity or trauma. This deformity was probably causing the wear out of their hip joint. These patients desire their leg length difference corrected. The surgeon can (to a certain degree) to lengthen the shorter leg. This is a desired leg leg lengthening.
The majority of the patients with leg length difference problems have, however, had equally long legs before the surgery. In most cases the surgeon increased (less often diminished) the length of the operated leg in these patients by the total hip operation inadvertently.
Often the lengthening is produced by a too long device (prosthesis) that was used by the surgeon to achieve a stable total hip joint.
The too long total hip - its femoral component is causing strain in the soft tissues and nerves around the operated on hip, in the spine spine, and in the other hip, resulting in pain. These patients continue to have pain even if the shorter, opposite leg will get a sole inlay to make the leg length equal. In this situation the patients are dissatisfied.
In some (few) patients the leg may become shorter after the surgery; the shortening of the leg is usually tolerated better because no soft tissues are strained. When compensated by appropriate shoe lift these patients do not have undue strain on their soft tissues and the spine is well balanced.
How to measure the leg length?
In practice, there are three methods how to measure the leg length.
Picture: X-ray measurement of the leg length difference
1) Measuring on the X-ray picture of the whole pelvis and both hips.
There are more methods how to ascertain whether the total hip replacement changed the length of the operated leg. (It is supposed that both legs were equally long before the surgery)
1)The surgeon measures the distance between the lover end of the hip joint (so called teardrop) and a point on the thigh bone called trochanter minor. The distance between these two structures gives the true difference in leg lengths (provided that the thigh- and shinbones are equally long).
2)The surgeon measures the distance from the centre of the ball component respective femoral head (upper line) to the trochanter minor (lower line). You see that on both sides these distances are equal.
3) The surgeon puts a line through the trochanter minor of both legs (the lower line) and another line through the lowermost part of the pelvis (the upper line). You see that both lines are parallel so the legs are equally long.
When discussing the leg length with your surgeon ask him to make similar measurements on x-ray picture of your hips.
2) Measuring on whole-leg x-ray pictures.
When the surgeon suspects that even thighbone and/or shinbone may be shorter (or longer) such as after childhood fracture, he orders the whole-leg x-ray pictures and measures the leg length on these pictures. On these special pictures a special measuring band is put beside the legs and is x-rayed together with them. This very precise method is not routinely used for measuring leg length after total hip surgery.
3) Measuring the leg length directly (without x-ray pictures).
On a patient lying supine, the surgeon / PT measures with tape (measuring - band) the distance from a protruding point on the upper pelvis (called spina illiaca) to another protruding point on the inner ankle joint. The error of this measurements is about 0,5 to 1,0 cm.
Picture: measuring the leg length with tape
click on the icon for a full size picture
Alternatively, on a standing patient, the surgeon / PT observes / palpates the spinal curvature and the slanting of the pelvis. He / she then puts successively higher blocks under the heel of the shorter leg, until the spinal curvature / slanting of the pelvis disappears. The height of the block indicates the shortening.
The apparent leg length discrepancy
The patient feels that one leg, usually the not operated leg, is shorter, although both legs are equally long as the measurement on the X-ray picture shows.
Picture: Apparently leg length discrepancy
Click on the icon for a full size picture
On this picture, the patient feels that the right leg, where he has a total hip device, is longer. Both legs are, however, equally long.
The cause of the apparent leg length difference is the contracture ( permanent shrinkage) of the soft tissues and of the abductor musculature (the gluetus and tensor fasciae muscles) around the operated on right total hip joint. The shrunken muscles and tissues on the right side slant the pelvis to the operated right total hip side. The slanting pelvis lifts the left leg (L), which feels shorter.
The spine, which must compensate for the slanting pelvis, is deformed.
The walking is awkward, the spine is curved, the patient has pain not only around the operated hip, but also in the back and in the other hip.
The complaints are often not in relation to the relatively small degree of pelvic slanting. It is the tension in soft tissues, not the apparent leg length difference, that causes pain.
The causes of the apparent leg length discrepancy
Often the occurrence of apparent leg length discrepancy may be anticipated before the surgery and the patient should then be informed about the risk of apparent leg length discrepancy already before the surgery. (Longjohn 1998).
Picture: replacement of a collapsed femoral head may cause apparent leg length discrepancy
Click on the icon for a full size picture
One example where lengthening may be anticipated is the patient with severe osteoarthritis of the hip joint that caused collapse of the femoral head (upper picture).
The femoral head in these patients eventually collapses and becomes smaller; the muscles around the collapsed femoral head, mainly the muscles that abducts the leg, eventually adapt to the shorter distance and become shorter too.
When the surgeon removes such arthritic hip joint and replaces it with a femoral component of normal length (lower picture), the short and tight abductor muscles cannot adapt immediately to the longer head and neck length. Instead, when the patient stands on the operated leg, the contracted muscles pull the pelvis to the operated on hip joint's side. The operated on leg feels longer.
Another occasion is the slanting of the pelvis caused by a fixed spinal deformity that was present already before the total hip operation. The total hip operation cannot repair the fixed spinal deformity. This slanting of the pelvis then continues after the total hip operation but now, because the new total hip has good motion, the patient gets the feeling that the leg became longer. This feeling again may become troublesome.
How to treat it:
The simplest and most effective treatment of apparent leg length discrepancy is its prevention. The surgeon should examine the tension in the muscles around the new total hip during the operation and make appropriate cuts in severely contracted tissues and muscles.
In patients with collapsed femoral heads as observed on the X-rays, the surgeon should inform the patient about the risk of temporary leg length discrepancy.
Most cases of apparent leg length discrepancy disappear during the three postoperative month after appropriate physical therapy and rehabilitation. A temporary heel and shoe lift may be used during this period.
In rare cases of severe contractures around the total hip causing pain, the surgeon may consider an operative treatment: The surgeon severs the tight tissues and lengthens the contracted muscles that impair the movement in the total hip joint.
Real, anatomic leg length discrepancy
Picture: Anatomic (real) leg length discrepancy because of a too long femoral component
Picture: X-ray picture of this situation
Click on the icon for a full size picture
After total hip replacement the right leg (R) is now longer than the opposite leg. This is due to the too long femoral component. The pelvis is slanting away from the operated side, the muscles around the total hip are stretched, and the spine is deformed. Notice how the too long femoral component stretches the muscles, ligaments, and nerves ! (not shown).
In well balanced total hip replacement, the center of the ball component should be level with the tip of the trochanter (the uppermost part of thigh bone). In this patient the center of the ball component is above the level of the tip of trochanter (right picture).
The tethered muscle, ligaments, and nerves explain the pain the patients with larger leg length difference have.
Small real leg length difference ( < 10 millimeters) after THR is usually well tolerated, because it causes almost no stretching of the soft tissues and only small spinal deformity.
There are basically two mechanisms why the surgeon can create a too long leg after total hip replacement even in patients without preoperative deformities in the hip joint:
In some patients the surgeon placed the cup component in wrong direction and then has had difficulty to get the total hip joint stable. Under assumption that the laxity has been caused by soft tissue laxity, the surgeon then chose a too long femoral component to strengthen the soft tissues.
In other patients the surgeon placed the cup component too low (distally) so that the whole new total hip has been seated too low in the pelvis. With the shift of the centre of the new total hip joint the whole leg moved "longer down".
(Parvizi 2003)
No amount of rehabilitation can make the shorter leg longer. If there is feeling of leg length inequality, the shorter leg must be lengthened by heel or shoe rise. But the "lengthening" of the other (healthy) leg may not remove the stretching of the soft tissues. Then only revision operation with an appropriate and appropriately placed component will help.
Reference:
Parvizi J et al.: J Bone Joint Surg-Am 2003; 85-A: 2310-17
Risk factors for real leg length discrepancy
Congenital Hip Dislocation. The leg of the patient with an inborn dislocation in one hip joint is shorter. (See the chapter Hip disease) . It may be technically impossible to lengthen the leg during the total hip surgery and the leg then may remain shorter.
Revision operation with slack tissues around the hip joint. In revision operation, the soft tissues may be damaged and slack from the previous failed total hip replacement. The surgeon may be forced to use a femoral total hip component with a long neck to strengthen the slack soft tissues around the hip joint. This will lengthen the leg.
An alternative is to use a femoral component with a longer lateral offset. (See the chapter Construction of a total hip prosthesis). The total hip prosthesis with longer offset will stretch the tissues around the hip without lengthening the leg too much.
Leg already shorter before the surgery for whatever cause, fracture healed in bad position for ex. It may be difficult to get such leg equally long after a total hip replacement.
Position of the patient on the operation table. If the patient is lying on his back (supine) on the operation table, the surgeon can compare (measure) directly the length of both legs during the operation.
Many surgeons carry out the total hip replacement with the patient lying on his / her side. In this position the surgeon cannot directly check and compare the length of both extremities during the operation. Preoperative planning and measurement devices are then most important.
There are countless devices on the market that facilitate the preoperative planning and help the surgeon to achieve equal leg length during total hip surgery.
When does the unequal leg length cause problems?
Studies demonstrate that the real leg length discrepancy does not cause problem in itself. It is the increased painful tension in muscles and nerves around the total hip joint and in the spine caused by the longer leg that causes pain. Unequal leg length after total hip replacement, well corrected by a shoe or heel rise,without muscle contractures, does not influence patient's satisfaction according to some authors. (White 2002) But not all surgeons and patients (!) agree.
What are the patient complaints?
The patients complain of a sense of imbalance and they feel that one leg is longer. The patients also have pain, that may be felt around the operated hip joint, in the groin, and /or in the lower back. But the pain may occur also in the opposite hip, especially if there is osteoarthritic damage of this hip apparent on X-ray pictures.
In patients with really longer operated leg, there may be pain and numbness caused by stretched nerves.
How to treat it:
The simplest and most effective treatment of the real leg length discrepancy after a total hip replacement is heel and shoe lift. In rare cases, however, the surgeon may be forced to change the femoral or cup component to achieve an appropriate leg length and remove the pain.
In patients operated on for unequal leg length, there may emerge a problem of hip stability: the muscles and ligaments once overstretched become slack after the corrective operation. In that case the surgeon should use a special cup component that may prevent dislocation.
References:
Woolson et al. J Arthroplasty 1999; 14: 159-64
Bose WJ. Orthopedics 2000; 23: 433-6
Longjohn D et al.: J Arthroplasty 1998;13: 97-100
Ranawat Ch. J Arthroplasty 1997;12: 359-65
White TO, Dougall TW : J Bone Joint Surg-Br 2002; 84-B:335-9
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