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Better methods to measure, image anatomy will advance science of joint replacement
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More than 1 million joint replacement surgeries will be performed in the United States in 2015, with the most common procedures being related to knee replacement. Despite a percentage of patients who are not satisfied with their outcomes, improved understanding of 3-D anatomy and the surrounding soft tissues has led to significant changes in the surgical techniques used to preserve and protect the normal anatomy while replacing deformed and arthritic joints.
With a consistent drive to improve treatment results, the analysis of currently developed systems suggests much technology has been relatively stable during the past decade. Improvements in outcomes are less likely to come from major innovations in implant design or surgical technique.
A possible exception is alternative bearing surfaces other than polyethylene. However, due to the cost and complexity of manufacturing these synthetic materials, as well as testing their ability to be safe and durable in weight-bearing or load-bearing human joints, significant change is likely to be a decade or more in the future.
Matching normal anatomy
Another area under extensive development is the use of patient-specific instrumentation (PSI). A high percentage of patients who have had excellent results after joint replacement have implants that match their normal anatomy and are well-fixed in a location that matches our opinions of ideal position. If we can consistently achieve these results when performing a joint replacement procedure, we should be able to improve overall results.
The process of PSI uses the most up-to-date technology, including accurate radiographs and CT scans, to define the patient’s true 3-D anatomy, followed by computer-assisted planning to prepare for the procedure and to create guides and instruments to reproduce preoperative plans with greater precision during surgery. Other benefits of the concept may include the ability to accurately match the patient’s anatomy with the prosthesis; more rapid intraoperative decisions to reduce OR time, blood loss and complications; more rapid rehabilitation due to the accuracy of reconstructing more normal joint kinematics; and improved overall outcomes, including less pain and better function. However, a recent meta-analysis was unable to show significant differences between PSI and standard instrumentation in critical outcome measures, including alignment of implants or mechanical axis of the joint or operation time.
Preoperative radiographic studies
Orthopedic surgeons often believe they could provide better service to patients if they could consistently place implants in the most anatomic position. In most cases, consistency is improved with the volume of cases performed. Orthopedic surgeons who perform lower volumes of joint replacement may have a more justifiable need to use PSI to reduce surgical “outliers” or deviations from normal anatomy. We have learned that the most significant improvement in a surgeon’s ability to reduce standard deviations from anatomic implant placement is at the beginning of the process by having time dedicated to analyzing preoperative radiographic studies and formulating well thought-out plans.
Despite advances in radiographic imaging, we still struggle to find a universal definition of some key measurements in joint replacement. This may be most significant in shoulder replacement, more specifically, with the glenoid. The most unreliable aspect of the surgery is glenoid replacement or resurfacing, which is responsible for most revision shoulder arthroplasties.
Recent studies have shown an association between placing the glenoid component in retroversion beyond normative values and the development of earlier signs of loosening of the glenoid component. Although revision rates for total shoulder arthroplasty remain less than 10% at 10 years, evidence of loosening of the glenoid component can be greater than 50% at 5-year follow-up. Empirically based reasoning suggests that if we can place and fix the glenoid component in the most anatomic position, then we would be able to minimize loosening and the risk of revision surgery. It seems logical that no matter what joint we are trying to reconstruct, precise placement of the joint replacement component would improve patient function and overall survival of the component.
The basics of anatomy and geometry of the scapula are presumably understood. We can measure angles, yet we continue to debate the best reference of the scapula to determine the true version of the glenoid with respect to the remaining scapular bone. Some of the debate is related to radiological shortfalls in the clinical setting where we have not been consistent in acquiring images of the entire scapula. Without the entire scapula, the reference point to determine glenoid version often may be different than what is determined when the entire scapula body is available for analysis.
The ideal reconstruction
With current PSI systems developed for the shoulder as well as other joints, the analysis of deformed and arthritic bones may be challenging with increasing severity of disease. The surgeon, technician or computer program has to select reference points to establish the calculations necessary to define alignment. Once reference points are established, the deformed joint is compared with normative data. Then guides and instruments are developed to restore the joint to fit normative data for patient populations, not specifically for that patient’s exact anatomy. The ideal reconstruction may be to restore the joint to match the patient’s lifelong anatomy or just to resurface the joint in its current alignment with minimal disturbance of the remaining bone. We do not have a clear answer in 2015.
As you will read in this month’s Round Table, the panelists disagree on the best method to reconstruct the glenoid for the treatment of glenohumeral arthritis. The conflicts are at every level of management, beginning with the need for specialized radiographic studies to analyze the glenoid deformity and version. Although many orthopedic surgeons acquire advance imaging, there is disagreement on the best method to determine the true version of the glenoid and how ambitious we should be to establish geometry that corresponds to normative data with a reconstructed glenoid. The added expense related to time, imaging and PSI has not been shown to affect outcomes.
Although proponents routinely note benefits, we have limited clinical data to support the program. Follow-up studies may likely show adverse events related to new concepts, such as augmented polyethylene devices that demonstrate inferior longevity due to osteolysis, or higher complication rates due to increased use of glenoid bone grafting, or the use of a reverse prosthesis in young active patients. Follow-up studies during the next 5 years to 10 years will provide further insight.
Future studies
We should not abandon PSI because early studies have not necessarily shown its value to care. In fact, the process should be ambitiously studied and evaluated to learn all the positive effects it may have in the future.
It is often stated, “if you can’t measure it, you can’t manage it.” We need better methods to measure anatomy, to image anatomy and to define the important geometry related to a patient’s joint architecture to advance the science of joint replacement. We are doing well with current joint arthroplasties, with most studies suggesting longevity of joint replacement of more than 10 years for 90% of patients. However, we can and must do better, especially for younger and more active patients and patients who live well beyond 10 years from the time of joint replacement.
It is appropriate to pursue methods that allow us to determine patients’ specific anatomy and then develop instruments and implants to match the specific anatomy as opposed to normative data. We need long-term follow-up studies to clearly define the best practices with respect to treatment of the arthritic and deformed joint.
- References:
- Sharareh B, et al. J Orthop Surg (Hong Kong). 2015;23(1):100-106.
- www.cdc.gov/nchs/fastats/inpatient-surgery.htm.
- For more information:
- Anthony A. Romeo, MD, is the Chief Medical Editor of Orthopedics Today. He can be reached at Orthopedics Today, 6900 Grove Rd., Thorofare, NJ 08086; email: orthopedics@healio.com.
Disclosures: Romeo reports he receives royalties, is on the speakers bureau and a consultant for Arthrex; does contracted research for Arthrex and DJO Surgical; receives institutional grants from AANA and MLB; and receives institutional research support from Arthrex, Ossur, Smith & Nephew, ConMed Linvatec, Athletico and Miomed.