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Faulty design increases the risk of neck fracture in a hip prosthesis
Nosrat Vatani1, Daniel Comando, José Acuña
1Hospital General de Agudos Dr. Juan Fernández, Buenos Aires Argentina.
Insights
A faulty design in Charnley type modular hip prostheses led to stem neck fractures in 9 patients, primarily men, after an average of 4 years. These fractures resulted from abnormal force transmission due to inadequate stem design, not material defects.
Area of Science:
- Orthopedic surgery
- Biomedical engineering
- Materials science
Background:
- Total hip arthroplasty (THA) is a common procedure to alleviate hip pain.
- The Charnley type modular 28 head prosthesis is a specific implant design used in THA.
- Implant failure, such as stem fracture, can lead to revision surgery and patient dissatisfaction.
Purpose of the Study:
- To investigate the cause of unexpected fractures in the neck of Charnley type modular stem prostheses.
- To determine if material defects or design flaws contributed to the observed fractures.
- To identify risk factors associated with these prosthesis failures.
Main Methods:
- Retrospective analysis of 35 total hip arthroplasties performed between October 1993 and May 1994.
- Examination of 9 fractured stem prostheses, including metallographic, chemical, and microhardness analyses.
- Correlation of fracture occurrence with patient demographics (gender, weight) and time to failure.
Main Results:
- Nine out of 35 (25.7%) Charnley type modular stem prostheses fractured at the neck.
- Fractures predominantly occurred in male patients (8 out of 9) after a mean of 4 years post-surgery.
- Analyses revealed no material abnormalities; fractures were attributed to an inadequate confluent radius causing abnormal force transmission.
- Higher patient load (men, heavy body weight) correlated with increased fracture risk.
Conclusions:
- The observed stem neck fractures are attributed to a faulty design of the Charnley type modular prosthesis, specifically an inadequate confluent radius.
- The design flaw leads to abnormal force transmission, increasing the risk of fracture, particularly in higher-load patients.
- Material analysis confirmed no inherent defects, reinforcing the conclusion of a design-related failure.
Abstract:
From October 1993 to May 1994, we performed 35 total hip arthroplasties (20 women) using a Charnley type modular 28 head manufactured by Medical Tee Brazil. 9 fractures through the neck of the stem prostheses occurred, all but 1 in men, after mean 4 (0.3-6) years. All fractures were due to an inadequate confluent radius causing abnormal transmission forces through the neck. The higher the load (men, heavy body weight), the greater the risk of fracture. The metallographic, chemical and microhardness analyses showed no abnormalities. We ascribe these fractures to faulty design of the stem prosthesis.