Total hip replacement surgery aims to relieve pain and restore function, but a potential outcome is a difference in leg length, known as leg length discrepancy (LLD). This is a common concern for individuals undergoing the procedure. While surgeons strive for symmetry, achieving equal leg lengths is secondary to ensuring the new hip joint is stable and functions correctly.
Causes of Leg Length Discrepancy
A perceived difference in leg length after surgery can stem from two sources: apparent and true discrepancy. An apparent LLD results from the body’s reaction to surgery. Factors like post-operative swelling, muscle tightness around the hip, or a temporary pelvic tilt can create the sensation that one leg is longer when no bony difference exists. These soft tissue issues often resolve as the body heals.
A true, or structural, LLD involves a measurable difference in the limbs. A primary objective for the surgeon is creating a stable hip joint that will not dislocate. To achieve this, it may be necessary to lengthen the operated leg by selecting specific implant components or adjusting their placement. This lengthening is a deliberate trade-off to ensure the new hip’s long-term stability and function.
Symptoms and Diagnosis
Patients with a leg length discrepancy often report feeling off-balance or lopsided, which can lead to a noticeable limp. This altered gait can contribute to pain in the lower back, sacroiliac joint, knee, or ankle as the body compensates. Some individuals may also experience muscle fatigue or strain around the hip.
The diagnostic process begins with a physical examination. The surgeon will observe the patient’s posture and gait, and may place wooden blocks of varying thickness under the shorter leg until the pelvis is level. This provides an initial estimate of the discrepancy and helps differentiate between a true and an apparent LLD.
For a precise measurement, imaging studies are the standard. A standing, full-length X-ray that captures both legs from the hips to the ankles, known as a scanogram, is the most accurate method. This allows for a direct comparison of the bone lengths and provides objective data in millimeters to guide treatment decisions.
Non-Surgical and Surgical Solutions
Following surgery, initial management for a perceived discrepancy is often observation. Surgeons recommend a “wait-and-see” period of three to six months for swelling to subside and tight muscles to relax. During this phase, a perceived difference can diminish or resolve on its own as the body heals.
Physical therapy is a key part of non-surgical management. A therapist can guide the patient through exercises to stretch tight muscles, like the hip flexors, which can contribute to a pelvic tilt. Strengthening the core and hip muscles also helps stabilize the pelvis and improve gait mechanics.
When a true discrepancy persists and causes symptoms, the most common intervention is a shoe lift. For smaller differences (less than two centimeters), an insert inside the shoe of the shorter leg is effective. For larger discrepancies, the shoe’s sole may need to be built up, which levels the pelvis and can alleviate associated pain.
In rare instances where the LLD is severe (greater than 20 millimeters), functionally limiting, and unresponsive to conservative treatments, revision surgery may be considered. The procedure involves replacing implant components to correct the length. This is a complex operation approached with caution due to the inherent risks of further surgery.
Prevention and Surgical Considerations
Preventing a significant leg length discrepancy begins before the operation. Surgeons use pre-operative templating, where they overlay images of prosthetic components onto a patient’s X-rays. This planning helps determine the optimal implant size and position to restore the hip’s biomechanics and anticipate changes to leg length.
To enhance precision during the procedure, surgeons employ various intra-operative techniques. They may use calipers to assess leg length in real-time or utilize intra-operative imaging, such as fluoroscopy, to visualize implant placement. Additionally, computer-assisted navigation systems are an advanced tool that can guide the surgeon for more accurate implant positioning.