Impact of knee flexion on patella length in osteoarthritic patients undergoing total knee arthroplasty.

PURPOSE: This study used magnetic resonance imaging (MRI) to evaluate in vivo preoperative changes in the length of the patellar tendon (LPT) in patients undergoing total knee arthroplasty (TKA). We sought to answer two questions: first, does the LPT change with flexion? Second, does the LPT show a gender-specific pattern?

METHODS

Eighty-five knees in 76 consecutive osteoarthritic patients were evaluated. The age range was 56-90 years (mean 70). The study included 62 females and 14 males. MRI was performed at full extension and at 30°, 60°, 90°, and full flexion.

RESULTS

There were significantly different patterns between genders (p < 0.001). The main shortenings occurred earlier, at 30°, in females and later, at 60°, in males. In females, LPT values in full extension were significantly longer than those measured at other flexion angles. In male subjects, significant differences in LPT values were found between full extension versus 90° (p < 0.001) and full flexion (p < 0.001), and between 60° versus 90°(p = 0.030) and full flexion (p = 0.030).

CONCLUSION

These differences might influence the gender-specific complications related to the extensor mechanism after TKA. These data provide useful information for surgeons attempting to achieve a satisfactory balance between joint gaps in the patellar reduced position intraoperatively.