Navigated shorter incision or smaller implant in knee arthritis?

Optimal intersurface stability for unicompartmental femoral component design with two pegs placed on the distal resection surface: 5 mm peg length increment and 10° peg inclination

PURPOSE

The present study aimed to identify the optimal design of the unicompartmental femoral component through parameter analysis and stability evaluation.

METHODS

A finite element (FE) analysis was applied to analyse and adjust the parameter combinations of the anterior tilt angle of the posterior condyle resection surface, the position of the peg, the length of the peg and the inclination angle of the peg, resulting in 10 different FE models. Setting three knee flexion angles of 8.4° (maximum load state during walking), 40° (maximum load state during stair climbing) and 90° (maximum load state during squatting exercise), quantitatively analysing the micromotion values of the bone-prosthesis interface and defining a weighted scoring formula to evaluate the stability of different FE models. The validity of the FE analysis was verified using the Digital Image Correlation (DIC) device.

RESULTS

The errors between the FE analysis and the DIC test at three flexion angles were 5.6%, 1.7% and 11.1%. The 10 different femoral component design models were measured separately. The FE analysis demonstrated that the design with a 0° anterior tilt angle of the posterior condyle resection surface, both pegs placed on the distal resection surface, lengthened 5 mm pegs and a 10° peg inclination angle provided the best stability.

CONCLUSION

The current study proposed a method for evaluating the stability of the femoral component design. The optimal intersurface stability design of the unicompartmental femoral component was achieved with two pegs placed on the distal resection surface, a 5-mm peg length increment and a 10° peg inclination. These results might provide a reference for the selection of unicompartmental femoral components in clinical practice and therefore improve the survival rate of future unicompartmental knee arthroplasty.

LEVEL OF EVIDENCE

Level III.

Computer-assisted unicompartmental knee arthroplasty using dedicated software versus a conventional technique

PURPOSE

The aim of this study was to retrospectively compare the results of two matched-paired groups of patients who had undergone a medial unicompartmental knee arthroplasty (UKA) performed using either a conventional or a non-image-guided navigation technique specifically designed for unicompartmental prosthesis implantation.

METHODS

Thirty-one patients with isolated medial-compartment knee arthritis who underwent an isolated navigated UKA were included in the study (group A) and matched with patients who had undergone a conventional medial UKA (group B). The same inclusion criteria were used for both groups. At a minimum of six months, all patients were clinically assessed using the Knee Society Score (KSS) and the Western Ontario and McMaster Osteoarthritis Index (WOMAC) index. Radiographically, the frontal-femoral-component angle, the frontal-tibial-component angle, the hip-knee-ankle angle and the sagittal orientation of components (slopes) were evaluated. Complications related to the implantation technique, length of hospital stay and surgical time were compared.

RESULTS

At the latest follow-up, no statistically significant differences were seen in the KSS, function scores and WOMAC index between groups. Patients in group B had a statistically significant shorter mean surgical time. Tibial coronal and sagittal alignments were statistically better in the navigated group, with five cases of outliers in the conventional alignment technique group. Postoperative mechanical axis was statistically better aligned in the navigated group, with two cases of overcorrection from varus to valgus in group B. No differences in length of hospital stay or complications related to implantation technique were seen between groups.

CONCLUSION

This study shows that a specifically designed UKA-dedicated navigation system results in better implant alignment in UKA surgery. Whether this improved alignment results in better clinical results in the long term has yet to be proven.

A flat all-polyethylene tibial component in medial unicompartmental knee arthroplasty: a long-term study

PURPOSE

The aim of this study is to present the clinical and radiological results of a cemented unicompartmental knee arthroplasty (UKA) using a flat all-polyethylene tibial component at long-term follow-up, in a homogeneous group of patients with medial femoro-tibial knee arthritis.

METHODS

The study group included 53 knees in 51 patients who were treated between January 1998 and November 1999 using a flat all-polyethylene tibial component. The same surgical technique was used for all patients. Inclusion criteria included a diagnosis of atraumatic arthritis, pre-operative flexion greater than 100° with no flexion deformity, a varus deformity of less than 10°, and a body mass index (BMI) less than 35. A neutral mechanical axis was considered the end-point in all interventions. The patients were assessed clinically using the International Knee Society (IKS) and the functional scores at follow-up. Plain radiographs were used to determine the alignment of the mechanical axis at 5, 10 and 14.7-year follow-up. A radiographic analysis of loosening, based on the method described by the IKS, was performed and the degree of arthritic progression in the non-resurfaced compartment was also assessed.

RESULTS

At latest follow-up five patients had died and the data for three patients had not been collected. At final review four knees had undergone revision surgery and a further patient had declined a recommended revision TKA. The main indication for revision surgery was progressive aseptic loosening of the tibial component in female patients. No revisions were required because of arthritic progression in the lateral compartment. Over time the clinical outcomes did not show statistically significant differences. There was a significant worsening of the mechanical axis at the last follow-up compared with the results at five and ten year review.

CONCLUSIONS

This study demonstrated that, in primary arthritis involving the medial femoro-tibial compartment, UKA using a flat all-polyethylene component could be considered an effective surgical option. Attention should be paid to progressive worsening of the mechanical axis over time associated with progressive radiolucency especially in female patients.

LEVEL OF EVIDENCE

IV.

Bicompartmental knee arthroplasty of the patellofemoral and medial compartments

PURPOSE

Studies have shown that after total knee arthroplasty neither normal biomechanics nor function is obtained. Selective resurfacing of diseased compartments could be a solution. A narrative review of the available literature on bicompartmental arthroplasty is presented.

METHODS

A literature review of all peer reviewed published articles on bicompartmental arthroplasty of the knee was performed. Bicompartmental arthroplasty is by definition the replacement of the tibiofemoral and the patellofemoral joint. It can be performed with a modular unlinked or a monolithic femoral component.

RESULTS

Bicompartmental arthroplasty performed with modular components obtains good to excellent results at ± 10 years follow-up. Function and biomechanics are superior to total knee arthroplasty. Modern monolithic femoral components are reported to give early failure and high revision rates and should be avoided.

CONCLUSION

Modular bicompartmental arthroplasty is an excellent alternative to treat bicompartmental arthritis of the knee leading to good functional results and superior biomechanics in well-selected patients. Caution is needed since only a few peer reviewed articles with small series and old implant designs are available on this type of arthritis treatment. Survivorship in these studies is inferior to total knee arthroplasty.