Femoral component rotation in patellofemoral joint replacement: a study protocol for a prospective observational study

[When nothing else works: patellofemoral joint arthroplasty]

Patellofemoral joint replacement is the best treatment option available for isolated patellofemoral arthritis. Especially young patients should be operated on with bone-sparing techniques that also preserve the soft tissues, since these patients are very likely to be revised at some point in their lifetime. Correct patient selection is important for the success of surgery and should include a meticulous clinical examination and imaging. Special attention should be paid to additional pathologies that may also need to be addressed. For the trochlea, there are two different options for treatment with the inlay and onlay system. The retropatellar surface should be replaced. Patellofemoral joint replacement is still rarely performed, so treatment in specialised centres is recommended. National joint registry data show high revision rates, while data from centres show promising results.

Hermes patellofemoral arthroplasty: Annual revision rate and clinical results after two to 20 years of follow-up

BACKGROUND

Patellofemoral arthroplasty (PFA) is an alternative to a total knee arthroplasty (TKA) in patients with severe isolated patellofemoral osteoarthritis. The main goal of this study was to determine the revision rate of the Hermes™ (Ceraver) anatomical unconstrained PFA.

METHODS

A retrospective single surgeon study was performed including all patients operated for PFA between 1997 and 2015. A standardized procedure was used to perform PFA with one type of prosthesis. All patients in the study were contacted at the final follow-up. The main judgment criterion was the annual rate of revision. Secondary criteria were the severity of anterior knee pain on a numerical scale (0-10) and functional scores (IKS and AKP scores).

RESULTS

During this period, PFA was performed in 64 patients (74 PFA), 52 women/12 men, mean age at surgery 59.6 ± 11.8 (31.3-82.1) years old. Four patients (5.4% of PFA) were lost to follow-up. Mean follow-up for the remaining 70 PFA was 7.5 ± 7.1 (2-20) years. TKA was required in 10 (14.3%) patients after a mean 5.4 ± 3.4 (1-9.3) years. The annual rate of revision was two-percent CI_95% [1.1-3.7%] if TKA was considered to be the defining event and 3.1% CI_95% [1.9-5.1%] for all types of revision (partial/total PFA replacement or TKA). Patients who underwent revision were significantly younger. After a mean eight (2-20) years of follow-up, mean anterior pain, the IKS and AKP scores improved significantly.

CONCLUSION

In this series, 78.6% of patients with a Hermes™ PFA did not require any revision after a follow-up of between two and 20 years.

LEVEL OF EVIDENCE

Level IV - retrospective study.

Femoral component rotation in patellofemoral joint replacement

BACKGROUND

Clinical outcomes in patellofemoral joint replacement may be related to femoral component rotation. Assessment of rotational alignment is however difficult as patients with isolated patellofemoral osteoarthritis often have trochlear dysplasia. The use of the medial malleolus as a landmark to guide rotation has been suggested. The purpose of our study was to evaluate this technique with regard to femoral component rotation, and to correlate rotation with clinical outcomes at one-year follow-up.

METHODS

Forty-one knees in 39 patients had patellofemoral joint replacement using the Zimmer Gender-Solutions patellofemoral prosthesis. Intraoperatively, we determined femoral component rotational alignment using an extramedullary rod aimed at the inferior tip of the medial malleolus. Postoperatively, we measured the angle between the femoral component and the anatomical transepicondylar axis using CT. The amount of rotation was correlated with clinical outcomes at one-year follow-up.

RESULTS

Forty knees in 38 patients were available for one-year follow-up. Mean femoral component rotation relative to the anatomical transepicondylar axis was 1.4° external rotation (range, -3.8 to 5.7°). We found no statistically significant correlation between femoral component rotation and change from baseline KOOS subscales at one-year follow-up.

CONCLUSIONS

Our findings show that when using the medial malleolus as a landmark to guide rotation, the femoral component of the patellofemoral prosthesis was oriented in external rotation relative to the anatomical transepicondylar axis in 80% of knees. Our study did not show a relation between the amount of external rotation and clinical outcomes.

LEVEL OF EVIDENCE

Level III.