Teriparatide Administration Increases Periprosthetic Bone Mineral Density After Total Knee Arthroplasty: A Prospective Study

BACKGROUND

Teriparatide is a currently available therapeutic agent for osteoporosis. Previous studies have reported that teriparatide affects periprosthetic bone mineral density (BMD) after total knee arthroplasty (TKA). However, little agreement has been reached concerning the treatment of periprosthetic BMD after TKA with teriparatide. Moreover, BMD in the femoral and tibial sides of the joints together has never been examined. We investigated the efficacy of teriparatide to inhibit BMD loss in the femoral and tibial side and considered complications such as migration and periprosthetic fractures after TKA.

METHODS

Twenty-two knees in 17 patients were included in this study, and a control group of patients who underwent TKA was identified according to their medical records. Dual-energy X-ray absorptiometry was performed for different locations (knee, hip, and lumbar spine), and regions of interest were measured to estimate BMD at initiation of the study as a baseline reference, followed by subsequent measurements at 6 and 12 months.

RESULTS

As a result of adjusting the difference between the BMDs of the 2 groups at initiation, there was a significant increase in R3 (posterior condyle) and R4 (lateral) at 6 months. Furthermore, there was a significant increase in R2 (anterior condyle), R3 (posterior condyle), and R6 (tibial diaphysis) at 12 months. The study group had a higher adjusted mean BMD in all regions than did the control group at 6 and 12 months.

CONCLUSION

Teriparatide may be a reasonable treatment option for osteoporotic patients to preserve or improve periprosthetic BMD after TKA.

[Proposal for an auxiliary tool designed to reduce retake rates for lateral radiography of the knee joint]

The reproducibility of lateral radiography of the knee joint in the lateral position is low because patient positioning can be easily affected by passive rotation of the knee joint. We calculated the correction angle of the femoral external rotation and the lower leg elevation and developed our own auxiliary tool for obtaining a lateral view image. We were able to obtain, in a single attempt, an image with misalignment of the condyle limited to less than 7 mm. Our tool also contributed to the reduction of the re-imaging rate, suggesting its usefulness in contributing to a lower re-imaging rate for lateral radiography of the knee joint.

Survival of medial unicondylar arthroplasties placed by one surgeon 1984-1998

Unicondylar arthroplasty survival rates have varied widely. Implant- and patient-specific factors may be contributory. One surgeon placed 411 medial compartment arthroplasties of 12 designs from 1984 to 1998. In most cases, the fixed bearing tibial component was placed with cement and featured gamma-sterilized-in-air polyethylene and a metal backing. Tibial component initial thickness averaged 8.5 +/- 1.4 mm. Polyethylene shelf age averaged 1.3 +/- 1.2 years. Age and weight at arthroplasty averaged 67 +/- 8 years and 83 +/- 15 kg, respectively. Survival (no revision) at 9 years was 80%. Revision was more common in younger patients, in those with a thinner tibial component or longer polyethylene shelf age, and when some designs were used rather than others; weight and gender were not associated with revision. Nine-year survival improved to 94% when tibial component thickness was > 7 mm and polyethylene shelf age was < 1 year (154 knees). Per our experience, placement of a thin or shelf-aged gamma-irradiated-in-air polyethylene bearing into a young or active subject could explain most failures of unicondylar arthroplasties done in the 1980s and 1990s. Unicondylar patients of that era who were fortunate enough to avoid a thin or aged oxidation-prone polyethylene bearing probably have enjoyed superior outcomes.

Patient, implant, and alignment factors associated with revision of medial compartment unicondylar arthroplasty

The investigators reviewed 245 fixed-bearing unicondylar arthroplasties that one surgeon performed as treatment of medial compartment osteoarthritis between 1988 and 1997 using a variety of cemented metal-backed tibial components and gamma-irradiated-in-air polyethylene bearings. Multivariate statistical analysis was used to evaluate how the event of revision was influenced by 3 patient factors, 3 implant factors, and 7 factors assessed from preoperative and early postoperative radiographs. Five factors were statistically associated with revision: (younger) patient age, (thinner) tibial component initial thickness, (longer) polyethylene shelf age, (lesser) angular reduction of medial tibial plateau varus, and (more varus) postoperative hip-knee-ankle angle. Besides illustrating deleterious consequences of using gamma-irradiated-in-air polyethylene in medial unicompartmental arthroplasty, our results support reducing varus angulation of the medial tibial plateau and knee at surgery.