Clin Orthop Surg.  2019 Dec;11(4):416-421. 10.4055/cios.2019.11.4.416.

Influence of Patellar Tilt Angle in Merchant View on Postoperative Range of Motion in Posterior Cruciate Ligament-Substituting Fixed-Bearing Total Knee Arthroplasty

• Chon J
• Jeon T
• Yoon J
• Jung D
• An CH

• KMID: 2462535
• DOI: http://doi.org/10.4055/cios.2019.11.4.416

Abstract

BACKGROUND
We investigated whether the patellar tilt angle influences the maximum knee flexion after total knee arthroplasty (TKA) performed by using a posterior cruciate ligament-substituting (PS) fixed-bearing prosthesis in patients with relatively loose or tight flexion gap.
METHODS
In this prospective cohort study, we followed up 169 patients for at least 2 years after TKA using PS fixed-bearing prosthesis. The patients were divided into two groups according to the flexion gap value"”calculated by subtracting the thickness of the final bearing from the flexion gap measured intraoperatively under 200-cN·m force after patellar reduction and insertion of the final femoral and tibial components"”into a relatively tight group (group T; 3-6.5 mm) and a relatively loose group (group L; 7-11 mm). Patellar tilt angles and maximum non-weight-bearing active knee flexion angles were assessed postoperatively. Group T was further divided into subgroup Tn if the patellar tilt angle was < 5° and subgroup Tw if the angle was ≥ 5°. Pearson correlation test was used for the correlation analysis of the flexion gap, patellar tilt angle, and postoperative flexion range.
RESULTS
The mean postoperative flexion was 137.3° in group T and 137.5° in group L. The mean patellar tilt angle was 6.5° in group T and 6.9° in group L. In group T, a strong negative correlation (r = −0.78, p < 0.05) was observed between the patellar tilt and postoperative flexion range. However, further analysis revealed that only the subgroup Tw showed a strong negative correlation (r = −0.76, p < 0.05). Significant correlations were not found in the subgroup Tn and group L.
CONCLUSIONS
In TKA where a relatively tight flexion gap (≤ 6.5 mm) is created because of concerns about postoperative flexion instability due to a loose flexion gap, the patellar tilt angle should be < 5° for maximal postoperative knee flexion.

Keyword

Arthroplasty knee; Flexion gap; Range of motion; Patellar tilt

MeSH Terms

Arthroplasty, Replacement, Knee*
Cohort Studies
Humans
Knee
Prospective Studies
Prostheses and Implants
Range of Motion, Articular*

Figure

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  Fig. 1 Flexion gap measurement method. (A) The flexion gap was measured under 200 cN·m force exerted by a tensor device and a torque driver. (B, C) The scale at the center of the tensor device balancer shows the balance between the medial and lateral gaps. We assembled a torque driver to the rack of the balancer and measured the gap distance across the two plates. (D) If the lateral gap is wider than the medial gap (unbalanced trapezoidal flexion gap), the white bar is not in parallel to the black bar due to the scissor effect on the tensor device. (E) However, when medial and lateral flexion gaps become equal after medial collateral ligament release, the white line is parallel to the black line on the tensor device in balanced quadrangular flexion gap.

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  Fig. 2 Patellar tilt was measured as the angle between a line connecting the medial and lateral corners of the patella and another line connecting the anterior apex of medial and lateral femoral component condyles.

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  Fig. 3 Measurement of self-passive flexion (A) and extension (B) angles of the knee. Using a goniometer, we measured the intersection angle between midlines in the thigh and leg.

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  Fig. 4 Correlation between postoperative flexion and patellar tilt in Pearson correlation test in group T: a strong negative correlation (r = −0.78, p < 0.05) was observed. Group T: the group with a relatively tight flexion gap (3–6.5 mm).

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  Fig. 5 Correlation between postoperative flexion and patellar tilt in Pearson correlation test in subgroup Tw. Of group T, the subgroup Tw with a patellar tilt ≥ 5° showed a strong negative correlation (r = −0.76, p < 0.05)

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