Advertisement for orthosearch.org.uk
Orthopaedic Proceedings Logo

Receive monthly Table of Contents alerts from Orthopaedic Proceedings

Comprehensive article alerts can be set up and managed through your account settings

View my account settings

Visit Orthopaedic Proceedings at:

Loading...

Loading...

Full Access

General Orthopaedics

Analysis of Outliers in Computer-Assisted Total Knee Arthroplasty

The International Society for Technology in Arthroplasty (ISTA)



Abstract

Computer navigation has been advocated as a means to improve limb and component alignment and reduce the number of outliers after total knee arthroplasty (TKA). We aimed to determine the alignment outcomes of 1500 consecutive computer-assisted TKAs performed by a single surgeon, using the same implant, with a minimum 1 year follow-up, and to analyze the outliers. Based on radiographic analysis, 112 limbs (7.5%) in 109 patients with mechanical axis malalignment of > 3° were identified and analyzed.

The indication for TKA was osteoarthritis in 107 patients and rheumatoid arthritis in 2 patients. Fifty-eight patients (53%) had undergone simultaneous bilateral TKA and 13 patients (12%) had a BMI >30. Preoperative varus deformity was seen in 100 limbs and valgus deformity in 12 limbs. Thirty limbs (27%) had an extra-articular deformity (2 post HTO limbs, 3 malunited fractures, 1 stress fracture, 21 severe femoral bowing and 3 tibial bowing) and 21 limbs (19%) had severe lateral laxity or subluxation. Thirty-eight limbs (34%) had a preoperative deformity of =10° and 24 limbs (21.5%) had varus or valgus deformity of >20°.

Postoperatively, 11 limbs were malaligned at ±3°, 74 limbs at ±4°, 22 limbs at ±5°, 2 limbs at ±6°, and 2 limbs at ±7°. Coronal plane malalignment of > ±3° of the femoral component was seen in 28 limbs, tibial component in 32 limbs, and both femoral and tibial components in 13 limbs. Twenty-six limbs with preoperative varus deformity had a postoperative valgus alignment of >183° and 3 limbs with valgus deformity had a postoperative varus alignment of <177°.

The incidence of outliers for postoperative limb alignment was low at 7.5% with the tibial component showing a higher incidence of coronal malalignment. Malalignment may be more common in cases of simultaneous bilateral procedures, preoperative limb alignment of =10°, limbs with extra-articular deformities and severe lateral instability. There was a tendency towards over-correction of the hip-knee-ankle axis in both varus- and valgus-deformed knees. Further detailed statistical analysis of the data will be presented.

This is the largest single-surgeon series of consecutive navigated TKAs and consequently the largest analysis of outliers that highlights which knees are likely to fall outside the +3 degrees of acceptable alignment and which therefore behoove the surgeon to exercise greater caution.


Email: