Limb lengthening common after total knee arthroplasty, study finds

SAN FRANCISCO — Patients typically experience an increase in limb length after undergoing total knee arthroplasty, according to a study presented here.

In particular, correcting preoperative valgus deformities can lead to larger increases in limb length vs. preoperative varus deformities, the study authors noted.

"Patients should be advised preoperatively about the likelihood of limb lengthening as a consequence of total knee arthroplasty (TKA)," they said in the study.

Jason E. Lang, MD, and colleagues investigated changes in limb length occurring after TKA performed in 102 knees of 98 patients. The investigators obtained full-length standing radiographs using a radiographic marker, and used the IMPAX digital radiography software (Agfa-Gevaert NV) to measure limb lengths and the mechanical and anatomic axes.

They displayed their results in a poster at the American Academy of Orthopaedic Surgeons 75th Annual Meeting.

Preoperatively, coronal alignment averaged 2.48° for the 102 knees overall and averaged 8.67° among 66 knees with varus alignment and 8.91° among 36 knees with valgus alignment.

After surgery, coronal alignment improved to average 0.98° overall and averaged 2.9° among preoperative varus knees and 1.06° among the preoperative valgus knees, according to the study.

Overall, 82 of the 102 knees (80.4%) experienced an increase in limb length after surgery, including 77% of the varus group and 86% of the valgus group.

The overall increase in limb length averaged 6.3 mm, with a mean increase of 5.17 mm for the varus group (P < .0001) and 8.38 mm for the valgus group (P < .0001), according to the study.

"This change in limb length results from the restoration of the joint space with the prosthetic components, as well as from a correction of the coronal and sagittal deformities commonly seen in patients with knee osteoarthritis," the authors wrote.

However, no correlation was found between limb lengthening and the type of prosthesis used — posterior stabilized vs. cruciate-retaining, they noted.

For more information:
Lang JE, Lonner JH, Scott RD, et al. Limb lengthening is a common consequence of total knee arthroplasty. P163. Presented at American Academy of Orthopaedic Surgeons 75th Annual Meeting. March 5-9, 2008. San Francisco.