Hip replacement surgery, or total hip arthroplasty, is a widely performed procedure to alleviate pain and restore mobility in damaged hip joints. While successful in improving quality of life, a potential outcome is a difference in leg length, known as leg length discrepancy (LLD). This condition, though subtle, can significantly affect comfort and function after the operation.
Understanding Leg Length Discrepancy After Hip Replacement
Leg length discrepancy (LLD) after hip replacement is when one leg appears shorter or longer than the other after the artificial joint is implanted. This difference can be either an actual anatomical variation in bone length or a functional discrepancy, where the perceived difference is due to factors like muscle tightness or pelvic tilt, without an actual change in bone length. While some pre-existing LLD is common in the general population, with many individuals tolerating small differences without symptoms, a new or exacerbated discrepancy after surgery can impact a patient’s biomechanics.
Even a small difference, sometimes a few millimeters, can be noticeable to patients and affect their balance and gait. The body often compensates for this unevenness, leading to various musculoskeletal issues. While a discrepancy of less than 10 millimeters is often well-tolerated by most patients, larger differences can cause significant discomfort and functional limitations. Lengthening of the operated leg is more frequently observed than shortening after hip replacement.
Common Causes of Leg Length Discrepancy
LLD after hip replacement can stem from pre-existing conditions and the surgical procedure. Prior to surgery, severe arthritis can lead to a shortening of the affected leg due to cartilage and bone loss within the hip joint. When the artificial joint restores the hip to its original length, it can create a sensation of the operated leg being longer, even if the legs are anatomically equal.
Surgical technique also plays a significant role in LLD. Surgeons aim to achieve equal leg lengths and proper hip stability during the procedure. However, the need to achieve joint stability often takes precedence, as a loose hip joint is at a higher risk of dislocation. To ensure stability, the surgeon may need to stretch the surrounding soft tissues, which can result in the operated leg being slightly lengthened. The size and positioning of the prosthetic components, such as the femoral stem and acetabular cup, also directly influence the final leg length.
Pre-existing conditions beyond arthritis, such as scoliosis or other spinal deformities, can also influence a patient’s body mechanics and contribute to a perceived or actual LLD after surgery. Additionally, muscle contractures around the hip and pelvis, often developed over years due to arthritis, can lead to a pelvic tilt, making one leg appear longer even if the bone lengths are equal. This “apparent” discrepancy may take time to resolve as the muscles adjust to the new hip alignment.
Recognizing Symptoms and Effects
Patients with LLD after hip replacement may notice various symptoms impacting daily activities and comfort. A common sign is a noticeable change in gait, often a limp, as the body compensates for unevenness. This altered walking pattern can lead to increased fatigue, especially after prolonged walking or standing.
Pain is another common symptom, localized to the hip, lower back, or knee on the longer side. This pain arises from the compensatory mechanisms the body employs, such as pelvic tilting or increased strain on muscles and joints. If the operated leg is significantly lengthened, nerves (sciatic, peroneal, or femoral) can become stretched, potentially causing numbness, tingling, or weakness in the leg, thigh, or foot.
Beyond physical discomfort, patients might also experience imbalance or instability, making them feel less secure. They may also visually observe one pant leg appears longer or their hips feel uneven when standing. While some initial sensations of unevenness are common as the body adjusts, persistent or worsening symptoms warrant evaluation.
Diagnosis and Treatment Approaches
Diagnosing LLD after hip replacement involves physical examination and advanced imaging. A healthcare provider performs a physical assessment to observe gait, posture, and estimate leg length differences. This clinical examination helps distinguish between a “true” anatomical LLD and an “apparent” LLD caused by soft tissue imbalances or pelvic tilt.
Imaging studies provide precise measurements of bone length and component positioning. Full-length standing X-rays, also known as scanograms or teleoroentgenograms, are commonly used, as they capture the entire length of both legs from hip to ankle, allowing for accurate measurement of bony discrepancies. In some instances, computed tomography (CT) scans may also be utilized for detailed assessment. Preoperative X-rays and templating, which involve using overlays of prosthetic components on X-rays, are also performed to anticipate and minimize LLD before surgery.
Treatment for LLD varies based on the severity of the discrepancy and the patient’s symptoms. For minor discrepancies, often less than 10 millimeters, conservative measures are typically the first line of approach. These include shoe lifts or orthotics worn in the shoe of the shorter leg to equalize the perceived length and improve comfort. Physical therapy, focusing on stretching and strengthening exercises, can also help address muscle imbalances and pelvic obliquity that contribute to functional discrepancies. Many functional discrepancies resolve within three to six months as the body adapts.
For more significant discrepancies, generally those exceeding 20 millimeters, or when conservative treatments fail to alleviate symptoms, surgical intervention may be considered. Revision surgery may involve adjusting the position or size of the implanted components, or in some cases, performing bone shortening or lengthening procedures. The decision for surgical correction is made collaboratively between the patient and surgeon, weighing the potential benefits against the risks of another operation.