Abstract
Introduction
We evaluated the utility of imageless computer-navigation coupled with a miniature robotic-cutting guide for managing large deformities in TKA. We asked what effect did severe pre-operative deformities have on post-operative alignment and surgery time using the system. We also report on the early functional outcomes of this group of patients.
Methods
This was a retrospective cohort study of 128 TKA's performed by a single surgeon (mean age: 71y/o [range 53–93], BMI: 31.1 [20–44.3], 48males). Patients were stratified into three groups according to their pre-operative coronal plane deformity: Neutral or mild deformity <10((baseline group); Severe varus ≥10(; severe valgus ≥10(; and according to the degree of flexion contracture: Neutral or mild flexion from −5(hyperextension to 10(flexion (baseline group); hyperextension ≤−5(, and severe flexion ≥10. (The degree of deformity and final postoperative alignment achieved was measured using computer navigation in all patients and analysed using multivariate regression. The APEX CR/Ultra Knee System (OMNIlife Science, Inc.) was used with the PRAXIM Navigation system in all cases. A students t-test was used to compare pre- and post-operative (3–6 months) Knee Society Scores (KSS) and Knee Functional Scores (KSSF) for all patients.
Results
Pre-operative coronal alignment ranged from 27(varus to 22(valgus and from 23° flexion to −17° hyperflexion. Postoperative alignment across all patients ranged from 2(valgus to 3.5(varus, and from 4(flexion to −4 (hyperextension. Mean post-operative alignment was 1.4(varus in the control group, 0.4(varus in the severe valgus group (p=0.004), and 1.8(varus in the severe varus group (p=0.111). Preoperative flexion, obesity, and gender had no significant effect on alignment accuracy or final extension. Mean tourniquet time for the control group was 48.8 minutes [95% CI: 45.3–52.4]. Severe varus knees took 4.8 minutes longer (p=0.006), while valgus knees took 2.9 minutes longer (p=0.260). Flexion contractures ≥10(and ≥15(increased tourniquet time by 3.8 minutes (p=0.152) and 10 minutes (p=0.033), respectively. Tourniquet time was slightly longer in obese patients by 3.2 minutes (p = 0.048) and was 6.3 minutes shorter for females than males (p<0.001). KSS and KSSF scores for all patients were: Pre-Op–KSS 18.7, KSSF 42.9; Post-Op (3–6 months) – KSS 97.6, KSSF 91.9. The improvement was significant (p<0.001) for both scores.
Conclusions
We have shown that in one surgeon's hands severe coronal deformities and flexion contractures can be consistently corrected to within 3° and 4° of neutral, respectively, when using computer navigation. The additional time required for managing these more difficult cases using this technology was typically 3–5 minutes.
