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General Orthopaedics

PRESERVATION OF ACETABULAR BONE STOCK IN TOTAL HIP ARTHROPLASTY USING CONVENTIONAL VERSUS ROBOTIC TECHNIQUES: A MATCHED-PAIR CONTROLLED STUDY

International Society for Computer Assisted Orthopaedic Surgery (CAOS) - 15th Annual Meeting



Abstract

Background

Preservation of acetabular bone during primary total hip arthroplasty (THA) is important, because proper stability of cementless acetabular cup during primary THA depends largely on the amount of bone stock left after acetabular reaming. Eccentric or excessive acetabular reaming can cause soft tissue impingement, loosening, altered centre of rotation, bone-to-bone impingement, intra-operative periprosthetic fracture, and other complications. Furthermore, loss of bone stock during primary THA may adversely affect subsequent revision THA.

Questions/Purposes

The purpose of this study was to compare preservation of acetabular bone stock between conventional THA (CTHA) vs. robotic-guided THA (RGTHA). We hypothesised that RGTHA would allow more precise reaming, leading to use of smaller cups and greater preservation of bone stock.

Methods

Patients who received RGTHA were matched to a control group of patients who received CTHA, in terms of pre-operative native femoral head size (47.8mm – 48.1mm), age (mean 56.9), gender, BMI, and approach. Acetabular cup size relative to femoral head size was used as a surrogate for amount of bone resected. We compared the groups according to three measures describing the acetabular cup diameter (c) in relation to the femoral head diameter (f). These three measures were: (1) c-f, the difference between the cup diameter and femoral head diameter, (2) (c-f)/f, the same difference as a fraction of the femoral head diameter, and (3) (c∧3-f∧3)/f∧3, the same ratio expressed volumetrically.

Results

A total of 57 matched pairs were included in each group. There were no significant differences between groups in terms of gender, age at surgery, or BMI. No differences in femoral head diameter or acetabular cup diameter were observed between groups (p > 0.05). However, measure (2) (c-f)/f and (3) (c∧3-f∧3)/f∧3 did differ significantly between the groups, with lower values in the RGTHA group (p < 0.02).

Conclusion

RGTHA allowed for the use of smaller acetabular cups in relation to the patient's femoral head size, compared to CTHA. Using acetabular cup size relative to femoral head size as a surrogate measure of acetabular bone resection, these results indicate that greater preservation of bone stock using RGTHA compared to CTHA. This may reflect increased translational precision during the reaming process. However, further studies are needed to validate the relationship between acetabular cup size and loss of bone in THA.