Patients achieved greater ROM at 1 year with increased flexion TKA device

Two patients in the increased flexion device group did not return to preop ROM vs. 12 patients in the standard component group.

A posterior-stabilized total knee arthroplasty prosthesis designed for increased flexion provided patients with significantly greater range of motion at 1 year compared to a standard posterior-stabilized device, a prospective study found.

Steven H. Weeden, MD, and colleague Robert Schmidt, MD, of the Texas Hip and Knee Center in Fort Worth, Texas, compared the range of motion (ROM) achieved between two groups of 25 patients. Both groups were implanted with a Nexgen [Zimmer] posterior-stabilized implant. However, investigators randomly assigned patients to receive either a standard femoral component or one designed with increased buildup on the posterior condyle and modified polyethylene in the anterior region, which is intended to decrease impingement with deep flexion, according to the study.

Randomization occurred after surgeons chose the tibial and femoral implant sizes and after nearly complete ligament balance, the authors noted.

The standard component group included 16 women and nine men who averaged 62.3 years of age. Preoperative ROM for these patients averaged from 2° to 121°. The modified component group included 15 women and 10 men who averaged 62.6 years of age and who had preoperative ROM averaging from 1.8° to 122°, according to the study, published in the Journal of Arthroplasty.

"There was no statistical difference in age, knee deformity, preoperative diagnosis or BMI between the two groups," the authors noted.

In all cases, surgeons performed primary total knee arthroplasty (TKA) using a mini-incision technique. All cases also involved similar pre- and postoperative protocols.

The researchers found that patients implanted with the modified component designed for improved flexion had significantly greater average ROM at 6 months and 1 year follow-up (P<.05). For these patients, ROM averaged from 0.6° to 130° at 6 months and from 0.6° to 133° at 1 year.

Comparatively, ROM for patients in the standard component group averaged from 0.8° to 120° at 6 months and from 0.6° to 120° at 1 year, according to the study.

Significantly more patients in the modified component group achieved flexion greater than 135° at 6 months and 1 year follow-up, the authors reported. In addition, only two patients in the modified component group did not return to their preoperative ROM compared to 12 patients in the standard component group, they noted.

The investigators did not see any significant radiographic differences between the two groups, and no patients experienced major complications.

"[Aside] from implanting a femur designed for increased flexion, all of the knees were prepared with an identical surgical technique. Moreover, the knees were sized and balanced before randomization," the authors wrote, noting that this allowed them to evaluate the effect of implant design specifically.

"This study shows that with a similar surgical technique in a similar group of patients, there is an improved degree of flexion at 6 months and at 1 year post-TKA with use of [posterior-stabilized] implants designed for increased flexion," they wrote.

For more information:

Weeden SH, Schmidt R. A randomized, prospective study of primary total knee components designed for increased flexion. J Arthroplasty. 2007;22:349-352.