Copyright © 2008 by The Journal of Bone and Joint Surgery, Inc.
Commentary & Perspective
Commentary & Perspective by
Thomas Parker Vail, MD*,
Department of Orthopaedic Surgery, University of California at San Francisco, San Francisco, California
Posted December 2008
There is universal agreement that achieving the maximal postoperative
range of motion following total knee arthroplasty is highly desirable, but the
role that implant design plays with regard to that outcome has been a source of
ongoing controversy. As the authors point out, one element of that controversy
has been whether preservation of the posterior cruciate ligament is associated
with improving the range of motion during the first two years postoperatively.
The authors of this study present a very carefully
constructed, controlled analysis of the role of posterior cruciate ligament
preservation versus substitution in a randomized, blinded, and prospective
study design. A team that included trained therapists measured and assessed the
patients with use of a reproducible technique for documenting range of motion
as well as other general outcome measures of pain and function. Other strengths
of the analysis include the multicenter patient accrual and multiple surgeon
contribution to the patient cohort, which might make the results more
applicable to the general practice of orthopaedic surgery.
An interesting and important part of the experimental design
was the a priori definition of a minimum measurable and clinically important
difference in range of motion. A 5° change in flexion or extension was chosen
by the authors as the minimum clinically important difference that could be
accurately measured. Although establishing a minimum clinically important
difference represents a very important and potentially quite powerful part of the
experimental design, this type of a priori analysis has not been used
frequently in orthopaedic device studies. This reality is partially explained
by the fact that a general consensus as to the minimum clinically important
difference in range of motion does not exist in the literature. For purposes of
statistical analysis, establishing that threshold is important but difficult to
do from a clinical perspective. Postoperative range of motion has been linked
to preoperative range of motion and cruciate ligament status in prior studies1-3.
The concept of how much motion is enough or how much change is adequate has not
been conclusively defined and may be a patient-specific threshold of
expectation.
Another strength of this study is the controlled analysis of
the specific devices that were chosen for comparison in the hands of the
surgeons who participated. Nevertheless, there are multiple subtle confounders in
this study design that are common in device studies and exceedingly difficult
to control. In particular, it is not clear whether the conclusions reached
relative to these specific implants will be generally applicable to other designs.
For example, while some studies have suggested that "high-flexion" knee
replacement devices do not enhance postoperative knee flexion, recent analysis
has suggested that certain changes in the design of specific components may in
fact be associated with better postoperative knee flexion4,5. In
considering the extent to which the findings of this study might be more widely
generalized to other designs, one must ask whether there are design features other
than posterior cruciate retention or posterior cruciate sacrifice that might
also impact the outcome. For example, there may be design-specific features
related to constraint, contour, or contact area that make the designs that were
studied distinctly different from other designs, limiting the general
applicability of the observations about the cruciate ligament alone.
Another important yet exceedingly difficult variable to
characterize is the surgeon experience with each technique. In considering the study
by Chaudhary et al., one might ask why it took longer for the surgeons to
perform the cruciate-substitution technique. Does this extra time suggest less
familiarity with the device or less familiarity with the technique? Alternatively,
did the surgeon's ability to balance the cruciate ligament during cruciate
retention affect the outcome for that cohort of patients? Finally, does the
experience of selected specialists from joint replacement centers in Canada
reflect the experience of surgeons elsewhere who may be doing a lesser volume
of joint replacement?
On balance, this is a very commendable study that helps to
set a higher bar for quality of orthopaedic device studies. Because the study
is so well focused, it does provide relatively strong evidence to refute any
claim of superiority of the cruciate-retaining or the cruciate-substituting
design in the hands of the surgeons who participated, or possibly in the hands
of surgeons with similar experience. The overall excellent results do support
the concept that it is possible to achieve equal success with use of very
different designs and techniques in knee replacement.
*The author did not receive any outside funding or grants in support of his research for or preparation of this work. The author, or a member of his immediate family, received, in any one year, payments or other benefits in excess of $10,000 or a commitment or agreement to provide such benefits from a commercial entity (DePuy). No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the author, or a member of his immediate family, is affiliated or associated.
References
1. Parsley BS, Engh GA, Dwyer KA. Preoperative flexion: Does it influence postoperative flexion after posterior-cruciate-retaining total knee arthroplasty? Clin Orthop Relat Res. 1992;275:204-10.
2. Christensen CP, Crawford JJ, Olin MD, Vail TP. Revision of the stiff total knee arthroplasty. J Arthroplasty. 2002;17:409-15.
3. Bong MR, Di Cesare PE. Stiffness after total knee arthroplasty. J Am Acad Orthop Surg. 2004;12:164-71.
4. Argenson JN, Scuderi GR, Komistek RD, Scott WN, Kelly MA, Aubaniac JM. In vivo kinematic evaluation and design considerations related to high flexion in total knee arthroplasty. J Biomech. 2005;38:277-84.
5. Huang HT, Su JY, Wang GJ. The early results of high-flex total knee arthroplasty: a minimum of 2 years of follow-up. J Arthroplasty. 2005;20:674-9.
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