CALCAR COLLAR IS PROTECTIVE AGAINST EARLY PERIPROSTHETIC FEMORAL FRACTURES AROUND CEMENTLESS PRIMARY TOTAL HIP ARTHROPLASTY: A REGISTRY STUDY WITH BIOMECHANICAL VALIDATION

JN Lamb; J Baetz; P Messer-Hannemann; A Redmond; RM West; MM Morlock; HG Pandit

doi:10.1302/1358-992X.2019.6.030

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CALCAR COLLAR IS PROTECTIVE AGAINST EARLY PERIPROSTHETIC FEMORAL FRACTURES AROUND CEMENTLESS PRIMARY TOTAL HIP ARTHROPLASTY: A REGISTRY STUDY WITH BIOMECHANICAL VALIDATION

The British Hip Society (BHS) Meeting, Nottingham, England, 27 February – 1 March 2019.

JN Lamb
J Baetz
P Messer-Hannemann
A Redmond
RM West
MM Morlock
HG Pandit

CALCAR COLLAR IS PROTECTIVE AGAINST EARLY PERIPROSTHETIC FEMORAL FRACTURES AROUND CEMENTLESS PRIMARY TOTAL HIP ARTHROPLASTY: A REGISTRY STUDY WITH BIOMECHANICAL VALIDATION

Lamb J, Baetz J, Messer-Hannemann P, et al. CALCAR COLLAR IS PROTECTIVE AGAINST EARLY PERIPROSTHETIC FEMORAL FRACTURES AROUND CEMENTLESS PRIMARY TOTAL HIP ARTHROPLASTY: A REGISTRY STUDY WITH BIOMECHANICAL VALIDATION. Orthop Procs. 2019;101-B(SUPP_6):30-30. doi:10.1302/1358-992X.2019.6.030

Lamb, JN, et al. “CALCAR COLLAR IS PROTECTIVE AGAINST EARLY PERIPROSTHETIC FEMORAL FRACTURES AROUND CEMENTLESS PRIMARY TOTAL HIP ARTHROPLASTY: A REGISTRY STUDY WITH BIOMECHANICAL VALIDATION.” Orthopaedic Proceedings, vol. 101-B, no. SUPP_6, 2019, pp. 30-30., https://doi.org/10.1302/1358-992X.2019.6.030

Lamb, J., Baetz, J., Messer-Hannemann, P., Redmond, A., West, R., Morlock, M., & Pandit, H. (2019). CALCAR COLLAR IS PROTECTIVE AGAINST EARLY PERIPROSTHETIC FEMORAL FRACTURES AROUND CEMENTLESS PRIMARY TOTAL HIP ARTHROPLASTY: A REGISTRY STUDY WITH BIOMECHANICAL VALIDATION. Orthopaedic Proceedings, 101-B(SUPP_6), 30-30. https://doi.org/10.1302/1358-992X.2019.6.030

Lamb, J., Baetz, J., Messer-Hannemann, P., Redmond, A., West, R., Morlock, M. et al. (2019) “CALCAR COLLAR IS PROTECTIVE AGAINST EARLY PERIPROSTHETIC FEMORAL FRACTURES AROUND CEMENTLESS PRIMARY TOTAL HIP ARTHROPLASTY: A REGISTRY STUDY WITH BIOMECHANICAL VALIDATION.” Orthopaedic Proceedings, 101-B(SUPP_6), pp. 30-30. Available at: https://doi.org/10.1302/1358-992X.2019.6.030

Lamb, JN, J Baetz, P Messer-Hannemann, A Redmond, RM West, MM Morlock, and HG Pandit. “CALCAR COLLAR IS PROTECTIVE AGAINST EARLY PERIPROSTHETIC FEMORAL FRACTURES AROUND CEMENTLESS PRIMARY TOTAL HIP ARTHROPLASTY: A REGISTRY STUDY WITH BIOMECHANICAL VALIDATION.” Orthopaedic Proceedings 101-B, no. SUPP_6 (2019): 30-30. https://doi.org/10.1302/1358-992X.2019.6.030

Lamb J, Baetz J, Messer-Hannemann P, Redmond A, West R, Morlock M, et al. CALCAR COLLAR IS PROTECTIVE AGAINST EARLY PERIPROSTHETIC FEMORAL FRACTURES AROUND CEMENTLESS PRIMARY TOTAL HIP ARTHROPLASTY: A REGISTRY STUDY WITH BIOMECHANICAL VALIDATION. Orthop Procs. 2019 May 1;101-B(SUPP_6):30-30. https://doi.org/10.1302/1358-992X.2019.6.030

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Abstract

Background

Post-operative periprosthetic femoral fractures (PFF) are a devastating complication associated with high mortality and are costly. Few risk factors are modifiable apart from implant choice. The design features governing risk of PFF are unknown. We estimated the 90-day risk of revision for PFF associated with design features of cementless femoral stems and to investigate the effect of a collar on early PFF risk using a biomechanical in-vitro model.

Patients, materials and methods

337 647 primary THAs from the National Joint Registry (UK) were included in a multivariable survival and regression analysis to identify the adjusted hazard of PFF revision following primary THA using cementless stems. The effect of a collar in cementless THA on early PFF was evaluated in an in-vitro model using paired fresh frozen cadaveric femora.

Results

Prevalence of PFF revision was 0.34% (1180/337647) and 44.0% occurred (520/1180) within 90 days of surgery. Implant risk factors included: collarless stem, non grit-blasted finish and triple tapered design. In the in-vitro PFF model a medial calcar collar consistently improved construct stability and fracture resistance.

Discussion

During rotational injury the collar can load the calcar in compression increasing the force required for a fracture. This increases the force required to cause a PFF around a collared implant versus collarless implants. The calcar possibly acts as a check-rein which prevents excessive peri-prosthetic trabecular deformation in rotational injuries and may improve the resistance to loosening after high energy injuries which do not cause cortical fracture.

Conclusion

Analysis of stem design features in registry data is a useful method to identify implant characteristics which affect the risk of early PFF around cementless femoral stems. Calcar collar reduced early PFF risk and this was confirmed by biomechanical testing. This approach may be useful in the analysis of other uncommon arthroplasty failure modes.

Email: umjnl@leeds.ac.uk