Leg length discrepancy (LLD) after a total hip arthroplasty (THA) is estimated to occur in 1%-27% of cases and is one of the most common causes of malpractice litigation within orthopedics.

Lengthening of the operative limb during THA is most common, resulting in an anatomical and objectively measurable difference in leg length. This can be due to overcorrection of preoperative LLD or to achieve intraoperative stability in patients with minimal preoperative shortening from degenerative disease and maintained superior joint space.

LLD can also occur as a functional adjustment disorder with a perceived LLD by the patient in the postoperative period without an objectively measurable leg length difference. This perceived LLD may be transient and due to a correction of leg lengths of a previously shortened operative extremity from cartilage loss. Once leg lengths are corrected, muscle tightness and imbalance may ensue, giving the patient a perception of LLD.

Shortening of the operative extremity during THA may occur. This can lead to muscular imbalance and resultant instability and recurrent dislocation, possibly requiring operative correction.

Shortening of the operative extremity may also occur with femoral component subsidence, acetabular component subsidence or loosening, and asymmetric wear of the polyethylene liner. Femoral component fracture and femoral head fracture are less common.

Natural LLD is common in the general population and is typically asymptomatic with differences of less than 5 mm.

Notable length discrepancies between legs after surgery can result in tightness of muscle groups within the proximal leg and lower back. Patients also can present with hip instability, abnormal gait, neurological damage, pelvic pain, and spinal and back complications, traditionally on the side of the longer leg. Knee pain can be seen in either leg.

Templating is a key planning process for a THA, which takes preoperative LLD into account and produces a surgical plan for intraoperative component placement that may result in equal leg lengths. This preoperative templating is highly dependent on the quality of preoperative imaging such as pelvic rotation and tilt to estimate LLD, component sizes, and component positioning needed to equalize leg lengths to within approximately 2 mm. Intraoperative imaging such as fluoroscopy or radiographs may be used to estimate leg lengths with trial components in place.

There are THA scenarios in which equal postoperative leg lengths are difficult to achieve, which warrant specific preoperative discussion with the patient. This includes hip dysplasia with severe preoperative LLD, severe superior bone or femoral deformities, patients with minimal superior cartilage loss, and patients with equal leg lengths preoperatively.