Effect of posterior condylar offset in post operative range of motion in cruciate retaining and sacrificing TKR: A comparative analysis

Abstract

Background: Restoration of posterior condylar offset (PCO) during TKA is believed to be an important to improve knee kinematics, maximizing range of motion (ROM) and minimizing flexion instability. The aim of prospective study was to find out the role of PCO in post-operative ROM after cruciate retaining (CR) and cruciate sacrificing (CS) TKA.

Methods and materials: A total of 90 patients were divided into the CR knee group (49) and CS knee Group (41) intra-operatively by the surgeon based on the status of Posterior Cruciate Ligament. Preoperative and postoperative PCO was evaluated on true lateral knee radiographs. The ROM was measured pre operatively and post operatively at 4 weeks, 8 weeks, 3 months, 1 year and 2 years. Appropriate statistical tests were used and results were interpreted.

Results: The mean flexion angle was 113.86° in CR knees and 118.29° in CS knees with a significantly greater improvement observed for the latter group. Preoperative mean PCO was 35.08 mm in CR knees and 36.37 mm in CS knees, while the corresponding values post operatively were 32.74 mm and 34.88 mm respectively, at follow-up. In order to evaluate the relationship between change of PCO and postoperative improvement in range of flexion, we divided the patients into three sub groups according to the difference in pre and post-operative PCO. The first sub group had a difference in PCO ≤ 1 mm after surgery (CR: 5 and CS: 8), second sub group with a difference in PCO 1-3 mm after surgery (CR: 28 and CS: 26) and the third subgroup with a difference in PCO >3 mm after surgery (CR: 16 and CS: 7). Then a comparison of difference in PCO and post-operative range of motion was done in both CR knees and CS knees separately. The final post-operative range of motion (flexion) in CR knees was 117.6°, 115.93° and 109.06° for the three subgroups respectively. Similarly, the final post-operative range of motion (flexion) in CS knees was 116.12°, 118.81° and 118.86° for the three subgroups respectively. Thus a significant difference between three sub groups was observed in CR knees (P < 0.0001), while no difference was observed in the PS knees.

Conclusion: The postoperative decrease in posterior condylar offset by more than 3 mm decreases the post-operative ROM in CR TKA but not in CS TKA. So it is critical to preserve PCO in CR but perhaps not CS knees to ensure optimal ROM postoperatively.

Keywords: Cruciate retaining; Cruciate sacrificing; Posterior condylar offset; ROM; TKR; Total knee arthroplasty.

Fig. 1

Pre operative lateral radiograph of knee showing measurement of PCO.

Fig. 2

Post operative lateral radiograph of knee showing measurement of PCO.

Fig. 3

Comparison of difference in the ROM in different CS Knee subgroups (as per PCO).

Fig. 4

Comparison of difference in the ROM in different CR Knee subgroups (as per PCO).