Does the intra-operatively measured leg length correction compare to the post-operative radiograph in total hip replacement surgery?

Keywords total hip replacement, leg length discrepancy, leg length correction, vertical measurement system, comparative study, longitudinal study


Background: This study aims to analyse the accuracy of the Vertical Measurement System™ (VMS) in assessing the leg length correction (LLC) during total hip arthroplasty (THA) by comparing the intra-operative measurements to the radiographic measurements obtained six weeks post-operatively.

Patients and methods: A prospective cohort study was conducted in which patients undergoing primary THA were enrolled at two centres in Cape Town, over a period of 19 weeks. THAs were performed by four surgeons. Pre-operative leg length discrepancy (LLD) measurements were obtained in 92 patients. The VMS was used to predict intra-operative LLC, and this measurement was compared to the post-operative LLC measured on the six-week follow-up X-ray. These measurements were statistically compared using the Mann–Whitney U test.

Results: The difference between the intra-operative VMS calculation and the six-week radiological measurement was not significant (p>0.05), with the difference in their mean values being 0.1±3.3 mm. In the cohort, 82% of the patients (n=75) were within 5 mm of the target LLC, and 96% of patients (n=88) were within 10 mm of the target LLC. The mean absolute residual LLD at six weeks was 3.2±3.1 mm.

Conclusion: The intra-operative LLC measurement obtained using the VMS accurately predicts the six-week post-operative radiographic LLC measurement.

Level of evidence: Level 4

Author Biographies

Z Moonda, University of Cape Town

MBBCh(Wits), FC Orth(SA); Orthopaedic surgeon, Arthroplasty fellow, Department of Orthopaedic Surgery, University of Cape Town; Vincent Pallotti Hospital, Cape Town, South Africa

M B Nortje, University of Cape Town

MBChB(UCT), FC Orth(SA), MMed(Orth)(UCT); Consultant orthopaedic and arthroplasty surgeon, Department of Orthopaedic Surgery, University of Cape Town, Vincent Pallotti and Kingsbury Hospitals, Cape Town, South Africa

R Dey, University of Cape Town

PhD; Postdoctoral fellow, Faculty of Health Sciences, University of Cape Town, South Africa; Groote Schuur Hospital, Cape Town, South Africa

How to Cite
MOONDA, Z; NORTJE, M B; DEY, R. Does the intra-operatively measured leg length correction compare to the post-operative radiograph in total hip replacement surgery?. South African Orthopaedic Journal, [S.l.], v. 19, n. 4, p. 206-211, nov. 2020. ISSN 2309-8309. Available at: <>. Date accessed: 03 dec. 2020.

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