All CR knees developed progressive posterior translation without any significant impact on functional outcomes: study

Apart from infection, instability and implant wear are the most common reasons for revision surgery following total knee arthroplasty (TKA). Conventional cruciate-retaining (CR) designs, being less constrained than their modern counterparts, rely on the posterior cruciate ligament (PCL) for long-term stability and survivorship.

Nithin Thomas Philip et al conducted a study to evaluate the association between PCL degeneration and posterior tibial translation (PTT), to determine whether PTT progresses over time, and assess the impact of PTT on functional outcomes (instability symptoms) in CR TKA performed for osteoarthritis, where the PCL appeared macroscopically normal intra-operatively.

All CR TKA cases performed for osteoarthritis over a 6-month period were included. Histological assessment of the PCL was done to evaluate degeneration. PTT was measured via stress radiographs at 6, 12, and 18 months post-operatively. Functional outcomes were assessed using the Knee Society Score (KSS) at each follow-up. Statistical analysis was performed to determine associations between PCL degeneration, PTT progression, and functional outcomes.

The key findings of the study were:

• A total of 151 knees in 105 patients were assessed over a mean follow-up of 22.1 ± 3.2 months.

• Minimal, mild, and moderate PCL degeneration were found in 37, 101, and 13 knees, respectively.

• PTT increased significantly over time (p < 0.0001), from 5.9 ± 4.3 mm post-operatively to 12.5 ± 4.8 mm at 18 months, independent of the severity of PCL degeneration (p = 0.1).

• The mean functional KSS improved significantly from 31.5 ± 3.8 pre-operatively to 91.3 ± 2.2 at 18 months (p < 0.0001), irrespective of PCL degeneration or PTT grade.

• No significant correlation was observed between functional KSS and progressive PTT at 6 months (r = − 0.03), 12 months (r = − 0.10), or 18 months (r = 0.02).

The authors concluded that - “PCL degeneration was seen in all patients with osteoarthritis. The severity of this degeneration did not correlate with the knee function. Almost all CR knee developed a progressive posterior translation irrespective of severity of PCL degeneration at a tibial slope of 7 degrees. The grade of translation did not have significant impact on functional outcome. Though no mid-flexion instability symptoms were noted in our 151 knees, more follow-up and further studies are required to assess the conversion of PTT into instability. The study also has limitations with regard to absence of a comparative group in deriving more concrete conclusions.”

Further reading:

Progressive Posterior Tibial Translation in Conventional Cruciate-Retaining Total Knee Arthroplasty: An Observational Study in 151 Osteoarthritic Knees

Nithin Thomas Philip et al

Indian Journal of Orthopaedics (2025) 59:2149–2156

https://doi.org/10.1007/s43465-025-01481-8