Monday, March 31, 2014

Patient specific instrumentation - is it of value?

Component alignment during total knee arthroplasty with use of standard or custom instrumentation: a randomized clinical trial using computed tomography for postoperative alignment measurement.

These authors report the results of a randomized controlled trial in which CT scans were used to compare postoperative component alignment between patients treated with custom instruments and those managed with traditional instruments.  They compared in-hospital data and early clinical outcomes in 48 primary total knee arthroplasties randomized to arthroplasty with either standard instruments or with patient-specific instruments produced with use of data from preoperative computed tomography. The same surgeon performed all of the arthroplasties.

No significant differences were found between the study and control groups with respect to any clinical outcome after a minimum of six months of follow-up. The patient-specific tibial cutting block was abandoned in favor of a standard external alignment jig in seven of the twenty-two study knees because visual checking by the surgeon indicated that the cut indicated by the patient-specific block would be malaligned. 41% of the procedures with patient-specific instruments required deviations from the customized surgical plans because of the specifics of the bony and soft tissue anatomy of the knee that were not incorporated into the customized plan.

A detailed analysis of intent-to-treat and per-protocol groups of study and control knees did not show any significant improvement in component alignment, including femoral component rotation in the axial plane, in the patients treated with the custom instruments. The percentage of outliers-defined as less than -3° or more than 3° from the correct orientation of the tibial slope-was significantly higher in the group treated with use of patient-specific blocks than it was in the control group, in both the intent-to-treat (32% versus 8%, p = 0.032) and the per-protocol (47% versus 6%, p = 0.0008) analysis.

The authors concluded that there were no significant improvements in clinical outcomes or knee component alignment in patients treated with patient-specific cutting blocks as compared with those treated with standard instruments. The group treated with patient-specific cutting blocks had a significantly higher prevalence of malalignment in terms of tibial component slope than the knees treated with standard instruments.

Comment: This is a robust level I randomized controlled clinical trial. The disadvantages of the patient-specific instruments included (1) increased cost and radiation exposure of the CT scan, (2) production of the cutting blocks ($1500) and (3) a six week delay in the surgery for planning and production of the blocks. These results are consistent with a prior report.

There has been a study of the use of patient-specific instruments in total shoulder arthroplasty; it is reviewed here.

These studies call into question the value of this technology. Even if the increase in time, expense and radiation exposure results is a small improvement in component position, is that improvement associated with better clinical outcomes? Equally important is the question of whether patient-specific instruments helps experienced surgeons deal with routine pathology, helps inexperienced surgeons deal with routine pathology, or helps surgeons deal with complex pathology. This study indicates that the answer to the first and last questions is 'no'. In our practice of shoulder pathology, experience has taught that the management of complex pathology, such as the bad arthritic triad (BAT) requires the surgeon to make intraoperative decisions that cannot be anticipated preoperatively, such as the optimal glenoid preparation, the diameter, height and eccentricity of the humeral head prosthesis, and the need for a rotator interval plication. It is not apparent that patient-specific shoulder instruments can anticipate the steps necessary to achieve the balance of mobility and stability required.


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