, Paul D. Siney1 and Patricia A. Fleming1
(1)
The John Charnley Research Institute Wrightington Hospital, Wigan, Lancashire, UK
Since absolute rigidity does not exist in nature, fixation of components and, therefore, failure of that fixation – loosening – may not be possible to define in terms that are acceptable to all.
In order to understand the complexity and the clinical significance of component loosening in total hip arthroplasty, it may be of interest to consider two aspects of this method of treatment: the indications for the operation and the reasons for clinical success.
The indications are brought on by the mechanical breakdown of the articulation. The clinical presentation is hip pain [1] restriction of movement of the joint and the activity of the patient.
Clinical success in correctly selected patients, is primarily due to pain relief as a result of the operation; the natural symptomatic articulation is replaced with an artificial neuropathic spacer functioning within a foreign body bursa.
Activity level achieved as a result of the operation is not a feature of a particular type of arthroplasty; it is a reflection of patient selection. Patents with multiple disabilities never feature as anecdotal single case successes.
The operation imposes demands on the technical skills of the surgeon: exposure of the joint, preparation of the bony bed and fixation of the components. Component fixation and their loosening may, therefore, be thought of as a “by-product” of this method of treatment.
The implant, now functioning as part of the skeleton, alters the patterns of load transfer with strain shielding and strain concentration. This gradual process is asymptomatic.
Failure of component fixation – loosening is an unknown experience to the patient and the surgeon. It is commonly and erroneously assumed that clinical success indicates secure component fixation and that failure of fixation will become clinically symptomatic. (A quotation on the subject, recorded during one of the past orthopaedic meetings, may be of interest. “If it did not trouble the patient it could not be a problem to the surgeon” shows the lack of understanding of the problem). Being a process its onset may not be obvious, nor may it be continuous or uniformly progressive.
Progressive loosening leads to failures of the skeleton housing the implant. Such failures present late, are symptomatic, possibly sudden in onset and result in loss of bone stock or fracture! Having reached that stage, the original problem, which was basically restricted to the articulating surfaces, now becomes a problem involving the skeleton. The technical problems to be addressed are now more in keeping with trauma and tumour surgery and not merely with the failure of the articulation.
To understand these features of both the natural joint and the arthroplasty, is to appreciate that clinical results do not reflect the mechanical state of the arthroplasty. Good quality serial radiographs offer more valuable information. The consequences of this method of surgery must be understood and accepted by the surgeon, the patient, and the health service before the operation.
Radiographic Appearances and Clinical Results
Clinical practice is driven largely by symptomatic patients. Having established the diagnosis, instituted appropriate treatment and relieved the symptoms, it is assumed that the problem has been solved. Any further problems would be expected to present symptomatically. This is the teaching, training and our practice. Prevention, anticipation and early intervention lag very far behind.
It should come as no surprise that the same reasoning is often applied to total hip arthroplasty as a method of treatment for painful, arthritic hips.
The Correlation Between Radiographic Appearances and Clinical Results
The correlation between the radiographic appearance of the cup and the findings at revision has been established by Hodgkinson et al. [2]. It was, therefore, logical that the study should be extended further in order to examine the correlation between radiographic appearances of the arthroplasty and the clinical results. Could we rely on patient’s symptoms when anticipating mechanical problems after THA?
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