Patient-Specific total knee arthroplasty for valgus osteoarthritis results in the use of minimal thickness polyethylene liners in low constraint implants.

BACKGROUND

Correction of valgus knee deformity during total knee arthroplasty (TKA) can present numerous challenges. This study assessed the ability of a patient-specific knee design to allow easier intraoperative balancing of valgus knees in primary TKA.

MATERIALS AND METHODS

This study utilized a database consisting of de-identified computed tomography (CT) scans, low constraint knee designs (CR or PS), tibial and femoral implant dimensions, and implanted polyethylene (PE) thickness for all patients who underwent primary TKA with a patient-specific knee design provided by Conformis Inc. (Boston, MA, US). Data were analyzed for knee design, coronal deformity, native posterior and distal femoral offset, and PE thickness.

RESULTS

A total of 26,227 cases were included, of which 25% had valgus deformity. In the PS group, the thinnest available PE (6 mm) was used for 64% of varus cases and 68% of valgus cases (P = 0.004). There was no difference in the distribution of thin (≤ 8 mm) and thick (> 8 mm) PE between varus or valgus knees with 0-5 degrees or > 10 degrees of deformity. Knees with varus deformity of 5-10 degrees were more likely to receive a thick PE than knees with valgus deformity of 5-10 degrees. For the CR group, the thinnest available PE (6 mm) was used in 77% of varus cases and 76% of valgus cases (P = 0.12). There was no difference in the distribution of thin and thick PE between varus or valgus knees regardless of deformity. Over 99% of CR knees received PE with thicknesses 8 mm or less, regardless of degree of preoperative varus or valgus deformity.

CONCLUSIONS

These results indicate that patient-specific instrumentation in TKA can facilitate valgus deformity correction without requiring increased PE thickness to achieve balancing. Patient-specific knee designs may reduce the difficulty of valgus knee correction while allowing the use of minimal thickness PEs in low constraint TKA implants.