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. 2022:8:43.
doi: 10.1051/sicotj/2022043. Epub 2022 Nov 11.

Differences between two sequential uncemented stem sizes in total hip arthroplasty: A comparative biomechanical study and potential clinical implications

Katherine Wang  1 , Eustathios Kenanidis  2 , Khurram Suleman  1 , Mark Miodownik  1 , Mahsa Avadi  3 , David Horne  3 , Jonathan Thompson  3 , Eleftherios Tsiridis  2 , Mehran Moazen  1
Affiliations

Differences between two sequential uncemented stem sizes in total hip arthroplasty: A comparative biomechanical study and potential clinical implications

Katherine Wang et al. SICOT J. 2022.

Abstract

Background: Early failure of uncemented femoral stems associated with incorrect sizing is a known postoperative complication. Surgeons are often faced with the question of whether an uncemented stem of adequate stability or a larger-sized stem should be implanted, especially when the proximal femoral cancellous bone is adequate. The biomechanical effect of sub-optimal stem sizing in the femur remains unclear. This study investigated the mechanical behaviour of two sequential sized uncemented stems of the same type.

Methods: Six laboratory models of synthetic non-osteoporotic femora were randomly divided into two groups and implanted with either a nominal or oversized uncemented hydroxyapatite-coated nonporous titanium collarless stem. Stiffness, uniaxial strain, and pattern of strain distribution were measured under an anatomical one-legged stance.

Results: Oversized stems demonstrated a higher overall stiffness compared to nominal; however, this was not statistically significant. The nominal stem showed a higher strain in the neck and the proximal medial diaphyseal region. The oversized stem showed higher strains in the distal region around the implant tip.

Conclusion: Opting to use a larger stem may potentially increase primary stability, thus allowing safer early mobility. However, higher stiffness may lead to stress shielding, bone loss, and thigh pain in the long term. In addition, strains in the diaphysis and the tip of the stem may predispose to periprosthetic fractures, especially in osteoporotic bones, making this a relatable aspect for users and biomechanical loading. Given the wide range of complex factors that need to be considered when choosing stem size in uncemented THA surgery, this study's results should be interpreted cautiously.

Keywords: Biomechanics; Experimental; Stem size; Stiffness; Strain; Total hip arthroplasty (THA); Uncemented.

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Figures

Figure 1
Figure 1
Overview of the study. Experimental setup of total hip replacement (A), measurements obtained (B), and the two different stem sizes used (C). S1–S2 highlight the strain gauge attachment site on the stem, and B1–B5 highlight the strain gauge attachment site on the bone. Size 13 N = 3.
Figure 2
Figure 2
(A) Comparison of overall average stiffness between size 13 and 14 uncemented stem specimens based on the overall average. (B) Comparison of average stiffness between individual constructs of size 13 and size 14 stems. Asterisk (*) denotes the statistical difference between the two variables (P < 0.05).
Figure 3
Figure 3
Summary of the strain measurements taken from strain gauges on different locations of the construct under a 500 N axial load. Uncemented size 13 and size 14 hip stems compared. *Highlights the statistical difference between corresponding groups (P < 0.05).
Figure 4
Figure 4
Comparison between the pattern of maximum principal strain across the medial side of the bone, between the size 13 and size 14 group at 500 N axial load.
See this image and copyright information in PMC

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