Millions of individuals undergoing hip or knee replacement surgery may face an unexpected complication: leg length discrepancy (LLD), a condition where one leg becomes measurably shorter than the other. This can lead to significant pain, altered gait, and patient dissatisfaction.
While minor leg length differences are common from birth, a discrepancy of more than 10 millimeters (mm) after joint replacement surgery can cause problems. Studies indicate that a substantial percentage of patients develop LLD following these procedures. According to a 2019 study in The Bone & Joint Journal, 80% of knee replacement patients experience some degree of LLD. A 1997 study in HIP International found that nearly 10% of hip replacement patients are left with an LLD exceeding 10mm. More recent research published in Orthopaedics & Traumatology: Surgery & Research in 2024 tracked 100 knee replacement patients, with approximately a quarter showing a discrepancy of at least 10mm.
These discrepancies can result from various factors during surgery, including the size of the implant used and its placement within the bone. "It can be put in too high or too low," explained Alex Chipperfield, an orthopaedic surgeon at Benenden Hospital. In hip replacements, if the acetabular cup is positioned higher or lower than the natural joint, or if the femoral stem is placed deeper or more prominently in the thigh bone, leg length can be altered. Even when a hip is surgically corrected to its proper anatomy, if the other hip still experiences arthritic damage, the operated leg might feel longer due to the untreated hip's shortened state.
LLD can also arise from factors unrelated to surgery, such as being born with different length femurs or tibias, or from bone fractures. Functional LLD, where bone lengths are equal but one leg appears shorter due to muscle tightness, pelvic tilt, weak core muscles, flat feet, or joint stiffness, is another form. However, the impact of LLD following joint replacement surgery is a concern that orthopaedic specialists believe warrants greater patient awareness and surgeon communication.
Signs of LLD include lower back pain and a noticeable rolling gait. Liam Stapleton, a sports physiotherapist and orthotics specialist, suggests that patients should be screened for LLD after surgery, ideally by physiotherapists who manage post-operative care. He advocates for a rehabilitation program to strengthen core, hip, and leg muscles to help patients manage potential differences in leg length. In severe cases, revision surgery may be necessary to correct the joint.
Experts emphasize that surgeons should proactively inform patients about the risk of LLD prior to surgery. A recent report highlighted a case where the NHS paid out £85,000 to a woman whose leg was left 33mm longer than the other after a hip replacement due to poor surgical planning and the use of an undersized implant. This discrepancy, if uncorrected, could necessitate spinal surgery.
Patients who have undergone or are scheduled for hip or knee replacement surgery are advised to inquire about the risk of LLD and to insist on being screened for it post-operatively to ensure proper management and prevent potential long-term complications.