Millions of people undergo hip and knee replacement surgeries each year, often seeking relief from chronic pain and improved mobility. However, a notable percentage of these patients can develop leg length discrepancy (LLD), a condition where one leg becomes measurably shorter than the other following surgery. This complication, if undetected, can lead to persistent lower back pain, sciatic pain, and an altered gait, diminishing the intended benefits of the surgery.
Studies indicate that LLD is a common, though often overlooked, outcome of joint replacement procedures. A 2019 study in The Bone & Joint Journal found that 80% of knee replacement patients experience some degree of LLD. While minor discrepancies may go unnoticed, differences exceeding 10 millimeters can manifest as significant problems, according to orthopaedic surgeon Alex Chipperfield of Benenden Hospital. Research from HIP International in 1997 suggested nearly one in ten hip replacement patients are left with an LLD of more than 10mm, and a 2024 study in Orthopaedics & Traumatology: Surgery & Research noted that about a quarter of knee replacement patients had a discrepancy of at least 10mm, potentially explaining patient dissatisfaction.
LLD can arise from various factors related to the surgical procedure itself. The size and placement of the implant are critical. If a hip implant's cup is positioned higher or lower than the original joint, or if the stem is placed too deep or too shallow in the thigh bone, it can alter leg length. In cases where a patient has arthritis in the other leg or back, restoring one hip to its proper anatomy can make the operated leg feel longer, even if the bone length is unchanged, due to the shortening effect of the untreated arthritic joint.
Beyond surgical causes, LLD can also be congenital or develop due to other conditions. Some individuals are born with natural differences in femur or tibia length, while fractures or conditions like scoliosis, a curvature of the spine, can also lead to functional LLD. In functional LLD, bone lengths are equal, but muscle tightness, pelvic tilt, weak core muscles, flat feet, or joint stiffness can create the appearance of a shorter leg.
Symptoms of LLD, such as lower back pain and a rolling or 'rocking' gait, are often attributed to other causes, like the original condition necessitating the surgery. Liam Stapleton, a sports physiotherapist and orthotics specialist, advocates for increased awareness of LLD within the medical community and suggests that physiotherapists, who routinely assess patients post-surgery, are ideally positioned to screen for these discrepancies. He notes that surgeons may be hesitant to screen, potentially due to concerns about medical negligence claims.
Early identification and management of LLD are crucial. Orthotic inserts, often called heel lifts, can effectively compensate for leg length differences, restoring a balanced gait and alleviating pain. In severe or persistent cases, revision surgery may be considered to adjust or refit the joint implant. The author’s personal experience highlights the profound impact of unaddressed LLD, where years of sciatic pain following knee replacements were resolved only after a specialist identified and corrected a significant leg length discrepancy with an orthotic insert.
To mitigate the risk of post-operative LLD, patients scheduled for hip or knee replacement surgery are advised to discuss the possibility of LLD with their surgical team and insist on being screened for any discrepancy after the procedure. This proactive approach can help ensure patients achieve the full benefits of their joint replacement surgery and avoid the debilitating consequences of an uncorrected leg length difference.