Overhang can raise odds for pain after TKR

Study finds women had a fourfold increase in the risk of overhang compared to men in investigation.

Issue: Issue 2 2009

KOHALA COAST, U.S.A. — Total knee arthroplasties in which the femoral component overhangs the femur by 3 mm or more increases the probability that they will be painful, according to an orthopaedic investigator.

“Having an overhang of more than 3 mm in any zone increased the risk of having any pain by 80%,” Ormonde M. Mahoney, MD, said at Orthopedics Today Hawaii 2009, held here. Gender and age were not major factors in the correlation.

“We think this is a significant issue, and even though we are not talking about revision-causing pain, this is limiting function,” he said. “This is something that we should be aware of and something we should be harping on with the manufacturers.”

Same surgeon, prosthesis

Mahoney presented data from a series of 437 consecutive knees using the same device. All the surgeries were performed by a single surgeon between 2005 and 2006 using a high-flexion posterior stabilized device and an identical surgical technique. All patients received the same rehabilitation.

Overall there were 261 women and 176 men evaluated. They all were similar in their preoperative status in terms of alignment and pain between the genders, Mahoney said.

During each of the surgeries, Mahoney and colleagues recorded surgical data on ligament releases, bone resection thicknesses, and gap characteristics. Additionally, they measured the overhang of the femoral component by using a ruler in 10 zones, five zones on the medial and lateral sides of each component, after removal of all osteophytes, he added.

Ormonde M. Mahoney, MD, told attendees of Orthopedics Today Hawaii 2009 that an overhang of more than 3 mm in any zone increased the risk of having any pain by 80%.

Image: Beadling L,
Orthopaedics Today Europe

Both men and women

To assess postoperative knee function, clinical data were obtained from chart reviews at 2 months and 1 year. “Range of motion was measured visually using a long axis goniometer,” Mahoney said. “Pain was graded as none, mild, moderate or severe, based on a standardized question format designed to minimize the well-documented tendency of patients to under-report their pain.”

They then correlated the data with the overhang measurements that were made intraoperatively to assess the prevalence and risk factors of the overhang.

“In terms of prevalence, overhang was observed frequently in both men and women. The rate was 40% in men and 68% in women,” Mahoney said. “As the components got bigger, the overhang became more prevalent, regardless of sex. This is a design issue in terms of the aspect ratio of modern total knee replacements,” he said.

“Women had a fourfold increase in the risk of overhang and a fivefold increase in having an overhang of more than 5 mm relative to men, but both genders were involved,” he said

Other significant risk factors for overhang noted by the study included patients of shorter stature.

In terms of overhang consequences, it did not predict knee function or pain at 2 months, or predict knee flexion at 1 year, he reported.

For more information:

Ormonde M. Mahoney, MD, can be reached at Athens Orthopedic Clinic PA, 1765 Old West Broad St., Building 2, Suite 200, Athens, GA 30606 U.S.A.; +1-770-549-1663; e-mail: Mahoney@aocfoundation.org. He is an unpaid consultant to Stryker Orthopaedics.

Reference:

Mahoney OM. Gender vs. component fit. Presented at Orthopedics Today Hawaii 2009. Jan. 11-14, 2009. Kohala Coast, U.S.A.