This study aimed to investigate the relationship between changes in patellar height and clinical outcomes at a mean follow-up of 7.7 years (5 to 10) after fixed-bearing posterior-stabilized total knee arthroplasty (PS-TKA). We retrospectively evaluated knee radiographs of 165 knees, which underwent fixed-bearing PS-TKA with patella resurfacing. The incidence of patella baja and changes in patellar height over a minimum of five years of follow-up were determined using Insall-Salvati ratio (ISR) measurement. We examined whether patella baja (ISR < 0.8) at final follow-up affected clinical outcomes, knee joint range of motion (ROM), and Knee Society Score (KSS). We also assessed inter- and intrarater reliability of ISR measurements and focused on the relationship between patellar height reduction beyond measurement error and clinical outcomes.Aims
Methods
The two distinct surgical techniques for total knee arthroplasty (TKA) are gap-balancing technique (GB) and measured resection technique (MR). The aim of this study was to compare coronal stability of the knee after TKA with GB or MR. A total of 80 TKA cases with at least 6 months follow up (average 34.4 months) were evaluated. The MR group comprised of 33 patients with an average age of 73.1 years, while the GB group comprised of 47 patients with an average age of 74.4 years. Zimmer NexGen LPS Flex was used for all cases. Coronal stability of the knee was examined by varus-valgus stress X-ray at full extension and in the 90 degree flexed position as reported by Kanekashu et al (CORR 2005). X-ray measurement was performed using the FUJI diagnostic imaging system FS-V673. The varus-valgus stress X-ray test at full extension showed a laxity of 4.7 + 2.1 degrees in the MR group and 3.9 + 1.9 degrees in the GB group. No significant difference was detected between the two groups. On the other hand, the varus-valgus stress X-ray in the 90 degree flexed position revealed a laxity of 8.7+4.1 degrees in the MR group and 5.3 + 2.7 degrees in the GB group (p<0.01, Student's t-test). Of the 11 knees that showed laxity of >11 degrees in the 90 degree flexed position, 10 were from the MR group and only one from the GB group (p<0.01, Fisher's exact probability test). Furthermore, the postoperative clinical score assessed by Japanese Orthopaedic Association criteria was significantly better in knees with a coronal laxity of <10 degrees in the 90 degree flexed position compared to those with >10 degrees (82.7 + 6.8 and 77.3 + 8.5 in the GB and MR groups, respectively). In conclusion, GB may contribute to improved functional performance after TKA by providing better coronal stability of the knee in the 90 degree flexed position.
