TKR study showed better clinical results at 2 years for kinematic than mechanical alignment techniques

Issue: April 2015

LAS VEGAS — In results of a randomized controlled study presented at the American Academy of Orthopaedic Surgeons Annual Meeting, an individualized knee alignment technique for total knee replacement performed with patient-specific guides was associated with mean Oxford Knee Scores, WOMAC scores and combined Knee Society scores that were better than those for mechanically aligned knees treated with the same knee prosthesis.

Perspective from Stephen M. Howell, MD

“Although mechanical alignment is a long-standing widely accepted principle of total knee replacement, this study shows that alignment technique based on restoring pre-arthritic kinematics for each patient’s particular knee can produce significantly better results until 2 years with regard to pain, function and motion compared to mechanically aligned,” Harold G. Dossett, MD, of Scottsdale, Ariz., said. “Every 2-year clinical result was better in the kinematically aligned group,” he said.

Investigators randomized 88 patients (88 knees) scheduled for total knee replacement (TKR) into two groups of 44 patients who underwent TKR either aligned kinematically or mechanically.

Mechanical alignment involved the use of conventional instruments.

The same model of cruciate-retaining prosthesis was implanted in each knee and the patients, clinical care professionals and radiographers were blinded to the alignment method used for each patient.

All patients underwent postoperative MRI scans and their Oxford Knee Scores (OKS), WOMAC scores and combined Knee Society scores were obtained at various postoperative intervals through 2 years. When Dossett and colleagues looked at limb alignment, they compared hip, knee and ankle angles for both groups and found a mean alignment that was close to 0 in both groups. Dossett said it was 0.1º and -0.1 º in the kinematically and mechanically aligned groups, respectively.

They also found similar knee alignment for the two groups, and any differences in the limb and knee alignment between the groups were not statistically different. There was a difference between the groups for implant alignment, both for the femoral and tibial components, according to Dossett.

“The most important finding in our study was a very unexpected finding” that concerned the OKS and WOMAC pain scores, he said.

For patients in both groups who were pain free at 2 years follow-up, based on the OKS, “we saw the patients were 2.4 times more likely to be pain free at 2 years with a kinematically aligned total knee. Similarly, looking at the pain scores on WOMAC, we noticed that the patients were 3.8 times more likely to be pain free in our study if they had a kinematically aligned knee compared to mechanically aligned.” – by Susan M. Rapp

References:

Dossett HG, et al. Bone Joint J. 2014; doi:10.1302/0301-620X.96B7.32812.

Dossett HG, et al. Orthopedics. 2012; doi:10.3928/01477447-20120123-04.

Dossett HG, et al. Paper #315. Presented at: American Academy of Orthopaedic Surgeons Annual Meeting; March 24-28, 2015; Las Vegas.

Disclosure: Dossett reports no relevant financial disclosures.

Perspective

Stephen M. Howell, MD

A multicenter study reported a degree of dissatisfaction and residual symptoms following mechanically-aligned total knee arthroplasty that recent modifications in implant design and surgical technique have not improved, and that a kinematically-aligned total knee arthroplasty (TKA) showed a trend towards more patients reporting their knee to feel “normal.” Similarly and independently, Dossett’s level-1 randomized, clinical trial also showed kinematically-aligned TKA has better patient-reported satisfaction, pain relief, function and flexion then mechanically-aligned TKA. The concern with kinematically-aligned TKA is the average 2° varus inclination of the tibial component and the possibility of premature failure. However, at 6.3 years mean after kinematically-aligned TKA, varus alignment of the tibial component, knee and limb did not adversely affect implant survival or function in a study I and my colleagues conducted, which is in press. Collectively these studies support consideration of kinematic alignment as an alternative to mechanical alignment for performing primary TKA.

Stephen M. Howell, MD

Sacramento, Calif.

Disclosures: Howell is a consultant to and receives royalties from Zimmer and Biomet Sports Medicine for patented or proprietary technology. He is a consultant to Think Surgical and is on the American Journal of Sports Medicine and Orthopedics editorial boards.