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Tomasz Poboży

Posterior Tibial Slope After Total Knee Arthroplasty — Does It Affect Outcomes?

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Tomasz Poboży

Polish version · Joint Replacement — Literature for Clinicians

Changes in posterior tibial slope after total knee arthroplasty raise concern because they can influence flexion geometry and soft-tissue tension. A new analysis of 370 patients suggests, however, that in posterior-stabilised TKA, relatively small deviations within the range typically encountered in surgery do not translate into meaningfully worse functional outcomes.

Why is this study interesting?

Posterior tibial slope (PTS) is one parameter of tibial component alignment in the sagittal plane. Biomechanically, it can influence knee flexion, the flexion space and ligament behaviour. In practice, radiographic deviation from the planned slope is therefore sometimes treated as a possible explanation for a mediocre result after surgery. The authors examined whether this association could actually be detected in medium-term patient outcomes.

Question and methods

This was a single-centre retrospective cohort study of 370 patients who underwent primary cemented total knee arthroplasty using one posterior-stabilised implant design. Mean age was 71 years and mean follow-up was 64.6 months, with a minimum follow-up of 48 months.

PTS was measured on standardised lateral radiographs before and after surgery. Two observers performed the measurements independently and were blinded to each other’s results. Change in slope was analysed by direction, magnitude (up to 3°, 4–9°, and at least 10°) and a 5.47° cut-off corresponding to the mean absolute change across the cohort. Outcomes included pain, WOMAC, Knee Society Score, Oxford Knee Score, Forgotten Joint Score-12 and range of motion. Multivariable analysis was also performed.

Results

  • All patient-reported outcome measures improved significantly after surgery.
  • Neither the direction nor the magnitude of PTS change was associated with pain, function or overall clinical improvement; p was greater than 0.05 for all of these analyses.
  • A greater PTS was associated with statistically greater flexion: the coefficient was 0.53° of additional flexion for each 1° increase in PTS (p<0.001).
  • This difference in range of motion did not translate into better patient-reported outcomes.
  • Preoperative function remained the strongest predictor of postoperative outcome.

Clinical interpretation for an orthopaedic surgeon

The important distinction is between a measurable difference and one that matters to the patient. The association between PTS and flexion was statistically clear but small, and it was not reflected in any of the functional scores. The findings challenge the simple assumption that every few-degree sagittal-plane deviation must be the reason for a poor TKA result.

The study supports a broader assessment of the dissatisfied patient. Baseline function, pain, stiffness, instability, alignment in other planes, component rotation, soft-tissue condition, infection and expectations all need to be considered. PTS measured on a lateral radiograph is rarely a complete explanation on its own.

Limitations

  • The study was retrospective and single-centre, so it cannot establish causation.
  • It included only cemented TKA using one posterior-stabilised implant design; the findings should not automatically be extrapolated to cruciate-retaining, medially stabilised or other implant systems.
  • PTS was measured on conventional lateral radiographs, which do not fully represent three-dimensional component position and are sensitive to limb positioning.
  • The analysis does not answer questions about extreme malalignment, implant survivorship, aseptic loosening or outcomes beyond a decade.
  • Unmeasured confounding remains possible despite multivariable analysis.

What might this change in practice — and what does it not prove?

The findings may reduce the tendency to overinterpret a modest PTS deviation as the sole cause of an unsatisfactory result after posterior-stabilised TKA. They are not an argument for arbitrary tibial component positioning or for disregarding surgical planning. Nor do they prove equivalence between different PTS angles, because this was not a randomised study designed to demonstrate no difference.

Reference

Altun O, Ergişi Y, Özdemir E, Özihtiyar AA, Altıntaş M, Daşar U. The Effect of Posterior Tibial Slope Change on Functional Outcomes After Posterior-Stabilized Total Knee Arthroplasty: An Analysis of 370 Patients Who Had A Minimum 4-Year Follow-Up. Journal of Arthroplasty. Published online 9 September 2026. PMID 42716147. DOI: 10.1016/j.arth.2026.09.001. PubMed abstract.

Content prepared by: Tomasz Poboży - orthopaedic surgeon.

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