Novel Arthrometer may help Quantify Vivo Knee Laxity in Three Planes Following Total Knee Arthroplasty

Novel Arthrometer for Quantifying In Vivo Knee Laxity in Three Planes Following Total Knee Arthroplasty

Knee instability is a leading cause of dissatisfaction following total knee arthroplasty (TKA). Instability can involve abnormal laxity in multiple directions including varus-valgus (VV) angulation, anterior-posterior (AP) translation, and internal-external rotation (IER).

Quantitative and objective tools to measure knee joint laxity preoperatively and postoperatively in multiple planes of motion are limited. Most devices for quantitatively measuring clinical, in vivo laxity (ie, arthrometers) operate in a single plane. No existing arthrometer objectively quantifies knee laxity in all three of these directions.

David Z. Shamritsky et al conducted a study to verify the safety and assess reliability of a novel multiplanar arthrometer. The study was conducted at Hospital for Special Surgery, New York. It has been published in ‘The Journal of Arthroplasty.’

The arthrometer utilized a five degree-of-freedom instrumented linkage. Two examiners each conducted two tests on the leg that had received a TKA of 20 patients (mean age 65 years (range, 53-75); 9 men, 11 women), with nine and eleven distinct patients tested at 3-month and 1-year postoperative time points, respectively. AP forces from -10 to 30 Newtons, VV moments of ±3 Newton-meters, and IER moments of ±2.5 Newton-meters were applied to each subject’s replaced knee. Severity and location of knee pain during testing were assessed using a visual analog scale. Intraexaminer and interexaminer reliabilities were characterized using intraclass correlation coefficients.

Key findings of the study were:

• All subjects successfully completed testing.

• Pain during testing averaged 0.7 (out of possible 10; range, 0-2.5).

• Intraexaminer reliability was >0.77 for all loading directions and examiners.

• Interexaminer reliability and 95% confidence intervals were 0.85 (0.66-0.94), 0.67 (0.35-0.85), and 0.54 (0.16-0.79) in the VV, IER, and AP directions, respectively.

The authors commented - “In conclusion, we established a novel arthrometer that enables safe, time efficient, quantitative, and objective measurement of VV, AP, and IER knee laxities in a TKA population. Our arthrometer will enable research regarding laxity in multiple planes and their relation to clinical outcomes.”

Further reading:

Novel Arthrometer for Quantifying In Vivo Knee Laxity in Three Planes Following Total Knee Arthroplasty

David Z. Shamritsky, Erin E. Berube et al

The Journal of Arthroplasty 38 (2023) S190 - S195

https://doi.org/10.1016/j.arth.2023.02.030