2015 ISAKOS Biennial Congress ePoster #1424

Impact of Alignment Variability on Patient Function and Satisfaction

Stefaan Van Onsem, MD, Gent BELGIUM
Matti Slabbaert, Medical Student, Ghent BELGIUM
Rutger Callens, Medical Student, Ghent BELGIUM
Catherine Van Der Straeten, MD, PhD, Ghent, East-Flanders BELGIUM
Jan M. K. Victor, MD, PhD, Gent BELGIUM

Ghent University, Ghent, BELGIUM

FDA Status Cleared

Summary: A relation between the alignment of the Total knee implant and the patient reported outcomes, is a correct placement and alignment of the TKA crucial?

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Abstract:

Background

Patient satisfaction is an import goal of total knee arthroplasty (TKA). There is a growing interest in the relation between the alignment of the implant and the patient reported outcomes. This originates from the poor relationship between physician-based scores and patient reported outcomes. Hence, the latter should be given more emphasis.

Aim

Does a correct postoperative knee alignment result in higher patient reported outcome scores? Does the preoperative alignment of the knee have an influence on the postoperative patient reported outcome scores?

Material And Methods

This study includes patients above 55 years of age who were scheduled for a TKA at our centre and who had a pre- and postoperative low dose full-leg length computed tomography (CT) scan. Each included patient answered the Knee injury and Osteoarthritis Outcome Score (KOOS) and the new Knee Society Score (KSS), both preoperatively and at 3 to 6 months postoperative. From the CT scans, different angles were measured, both in 2D as in 3D. The used angles were: condylar twist angle (CTA), posterior condylar angle (PCA), hip-knee-ankle angle (HKA), tibialfemoral rotation angle (TFRA), posterior tilt of the tibial implant (STPA) and the frontal plane angle of the tibial implant (FTPA). Two groups were created, with values inside and values outside the reference area. (Reference areas: CTA: 5° internal rotation (IR), PCA: 3° IR, HKA: 0°, TFRA: 1° IR, FTPA: 0°, STPA: 3° flexion, each ± 3°)
Statistical analysis compared these two groups with the patient reported outcome scores. To analyse the direction
of the angle (above or below the reference area), three groups were created and were statistically compared with the patient reported outcome scores.

Results

From the limited number of patients (15) who already went trough the whole process, we were able to find a significant difference for the PCA. A value inside the reference area resulted in less symtoms (KOOS)(p=0,012), better KOOS total ADL (p=0,026), and a higher satisfaction (p=0,022). Analysis of the three groups showed a significant difference for the PCA when the implant was placed more in external rotation according to the reference interval: more symptoms (KOOS)(p=0,016), worse score for ADL (p=0,025) lower satisfaction (p=0,021). For the TFRA we found that the patient had more pain (p=0,043) and a lower QOL (p=0,038) when the tibial component was placed more into external rotation in reference to the femoral component. A multivariate regression analysis will be executed to calculate the impact factor of each angle on the PROMs. More patients will be included the upcoming weeks.

Conclusions

and clinical implications: We evaluated the influence of the alignment of a total knee implant on the patient reported outcome measures (PROM). Not only were we able to state that the outliers have an influence on the PROMs but also that little changes in the alignment can cause a difference in PROM. External rotation also lowers the PROMs.

We can conclude that a correct placement and alignment of the implant is crucial for the patient reported outcomes.