Is isolated insert exchange a valuable choice for polyethylene wear in metal-backed unicompartmental knee arthroplasty?

Supine Knee Positioning Does Not Interfere with Mobile-Bearing Unicompartmental Knee Arthroplasty Performance

The Food and Drug Administration has only approved mobile-bearing unicompartmental knee arthroplasty (MB-UKA) to be performed with a hanging leg holder. The purpose of this study is to evaluate the impact of a supine knee position on MB-UKA performance.In total, 16 cadavers were randomized so that either the right or left knee was placed in the flexed or supine positions. One board-certified orthopaedic surgeon and three adult reconstruction fellows that attended the required Oxford partial knee instructional course performed four operations in each position. The primary outcome was final knee balance. Secondary outcomes included procedure duration, timing of individual surgical steps, implant sizes, range of motion, implant alignment, and fracture. A Students t-test was used to examine differences between positions with significance set at p < 0.05. Secondary analyses using two one-sided tests were conducted to explore equivalence between the two positions.There was no significant difference in mean final balance between supine (1.7 mm ± standard deviation [SD] = 1.5 mm) and flexed (1.3 ± 1.3 mm) positions (p = 0.390). There were also no significant differences between positions for procedure time (p = 0.497), tibia coronal alignment (p = 0.614), tibial slope (p = 0.194), femoral component sagittal alignment (p = 0.091), and fractures (n = 0). Exploratory equivalence analyses indicated that the positions were equivalent for final balance (p = 0.002).MB-UKA performed in the supine position is not significantly different from the flexed position in terms of ligament balance, overall procedure time, and radiographic appearance. These initial safety data warrant further clinical investigations and support the expansion of the surgical technique to include performing MB-UKAs in the supine position.

Chronic Wear-Induced Bearing Dislocation in a Fixed-Bearing Unicompartmental Knee Arthroplasty: A Case Report

Case

We present a case of late onset, bearing wear-induced failure of locking mechanism, resulting in bearing dislocation and rapidly progressive severe metallosis in a medial fixed-bearing (FB) unicompartmental knee arthroplasty (UKA).

Conclusion

Bearing dislocation is a rare complication of chronic wear in FB UKA, and early recognition is essential to prevent metallic component articulation-induced metallosis and catastrophic failure.

Management of the Failed Medial Unicompartmental Knee Arthroplasty

With recent design modifications, proper patient selection, and sound surgical technique, medial unicompartmental knee arthroplasty has demonstrated long-term success in the management of degenerative joint disease. Nevertheless, complications do occur, most often aseptic loosening, tibial fracture, polyethylene wear, bearing dislocation, disease progression, infection, and unexplained pain. Some failures can be managed with retention of the implant, whereas others require revision to total knee arthroplasty (TKA), possibly including augments and stems. Although outcomes of unicompartmental knee arthroplasty may not match those of a primary TKA, they tend to exceed results of revision of a previous TKA.

Analysis of in-vivo articular cartilage contact surface of the knee during a step-up motion

BACKGROUND

Numerous studies have reported on the tibiofemoral articular cartilage contact kinematics, however, no data has been reported on the articular cartilage geometry at the contact area. This study investigated the in-vivo tibiofemoral articular cartilage contact biomechanics during a dynamic step-up motion.

METHODS

Ten healthy subjects were imaged using a validated magnetic resonance and dual fluoroscopic imaging technique during a step-up motion. Three-dimensional bone and cartilage models were constructed from the magnetic resonance images. The cartilage contact along the motion path was analyzed, including cartilage contact location and the cartilage surface geometry at the contact area.

FINDINGS

The cartilage contact excursions were similar in anteroposterior and mediolateral directions in the medial and lateral compartments of the tibia plateau (P>0.05). Both medial and lateral compartments were under convex (femur) to convex (tibia) contact in the sagittal plane, and under convex (femur) to concave (tibia) contact in the coronal plane. The medial tibial articular contact radius was larger than the lateral side in the sagittal plane along the motion path (P<0.001).

INTERPRETATIONS

These data revealed that both the medial and lateral compartments of the knee experienced convex (femur) to convex (tibia) contact in sagittal plane (or anteroposterior direction) during the dynamic step-up motion. These data could provide new insight into the in-vivo cartilage contact biomechanics research, and may provide guidelines for development of anatomical total knee arthroplasties that are aimed to reproduce normal knee joint kinematics.

Mid-Term Outcomes of Metal-Backed Unicompartmental Knee Arthroplasty Show Superiority to All-Polyethylene Unicompartmental and Total Knee Arthroplasty

BACKGROUND

Two commonly used tibial designs for unicompartmental knee arthroplasty (UKA) are all-polyethylene "inlay" and metal-backed "onlay" components. Biomechanical studies showed that the metal baseplate in onlay designs better distributes forces over the tibia but studies failed to show differences in functional outcomes between both designs at mid-term follow-up. Furthermore, no studies have compared both designs with total knee arthroplasty (TKA).

QUESTIONS/PURPOSES

The goal of this study was to compare outcomes of inlay UKA and onlay UKA at mid-term follow-up and compare these with TKA outcomes.

METHODS

In this retrospective study, 52 patients undergoing inlay medial UKA, 59 patients undergoing onlay medial UKA, and 59 patients undergoing TKA were included. Western Ontario and McMaster Universities Arthritis Index scores were collected preoperatively and at mean 5.1-year follow-up (range 4.0-7.0 years).

RESULTS

Preoperatively, no differences were observed in patient characteristics or outcome scores. At mid-term follow-up, patients undergoing onlay medial UKA reported significant better functional outcomes than those of inlay medial UKA (92.0 ± 10.4 vs. 82.4 ± 18.7, p = 0.010) and when compared to TKA (92.0 ± 10.4 vs. 79.6 ± 18.5, p < 0.001) while no significant differences between inlay medial UKA and TKA were noted. No significant differences in revision rates were found.

CONCLUSION

Functional outcomes following onlay metal-backed medial UKA were significantly better compared to inlay all-polyethylene medial UKA and to TKA. Based on the results of this study and on biomechanical and survivorship studies in the literature, we recommended using metal-backed onlay tibial components for unicompartmental knee arthroplasty.

Conversion of a unicompartmental knee arthroplasty to a total knee arthroplasty: can we achieve a primary result?

OBJECTIVES

Unicompartmental knee arthroplasty (UKA) is a potential treatment for isolated bone on bone osteoarthritis when limited to a single compartment. The risk for revision of UKA is three times higher than for total knee arthroplasty (TKA). The aim of this review was to discuss the different revision options after UKA failure.

MATERIALS AND METHODS

A search was performed for English language articles published between 2006 and 2016. After reviewing titles and abstracts, 105 papers were selected for further analysis. Of these, 39 papers were deemed to contain clinically relevant data to be included in this review.

RESULTS

The most common reasons for failure are liner dislocation, aseptic loosening, disease progression of another compartment and unexplained pain. UKA can be revised to or with another UKA if the failure mode allows reconstruction of the joint with UKA components. In case of disease progression another UKA can be added, either at the patellofemoral joint or at the remaining tibiofemoral joint. Often the accompanying damage to the knee joint doesn't allow these two former techniques resulting in a primary TKA. In a third of cases, revision TKA components are necessary. This is usually on the tibial side where augments and stems might be required.

CONCLUSIONS

In case of failure of UKA, several less invasive revision techniques remain available to obtain primary results. Revision in a late stage of failure or because of surgical mistakes might ask for the use of revision components limiting the clinical outcome for the patients. Cite this article: Bone Joint J 2017;99-B(1 Supple A):65-9.

Long-term results of compartmental arthroplasties of the knee

Partial knee arthroplasty (PKA), either medial or lateral unicompartmental knee artroplasty (UKA) or patellofemoral arthroplasty (PFA) are a good option in suitable patients and have the advantages of reduced operative trauma, preservation of both cruciate ligaments and bone stock, and restoration of normal kinematics within the knee joint. However, questions remain concerning long-term survival. The goal of this review article was to present the long-term results of medial and lateral UKA, PFA and combined compartmental arthroplasty for multicompartmental disease. Medium- and long-term studies suggest reasonable outcomes at ten years with survival greater than 95% in UKA performed for medial osteoarthritis or osteonecrosis, and similarly for lateral UKA, particularly when fixed-bearing implants are used. Disappointing long-term outcomes have been observed with the first generation of patellofemoral implants, as well as early Bi-Uni (ie, combined medial and lateral UKA) or Bicompartmental (combined UKA and PFA) implants due to design and fixation issues. Promising short- and med-term results with the newer generations of PFAs and bicompartmental arthroplasties will require long-term confirmation.

Cite this article: Bone Joint J 2015;97-B(10 Suppl A):9–15.