Women’s higher UKR revision rates possibly related to tibiofemoral angle differences

Patients who underwent unicompartmental knee replacement at a large U.K. joint replacement unit and required revision to a total knee replacement had the procedure at a mean of 28 months after their index surgery, according to a 6-year retrospective controlled study presented at the 2010 Meeting of the Combined Orthopaedic Associations in Glasgow.

The study also showed a 2.59% revision rate and that most revisions, particularly in women, were due to osteoarthritis (OA) disease progression in the lateral knee compartment.

Antony J.R. Palmer

Specialist registrar Antony J.R. Palmer, BMBCh, MA, MRCS, told Orthopaedics Today Europe, “We think the patients at greatest risk of failure are [women] in valgus alignment with isolated medial compartment osteoarthritis, as they are prone to be pushed further into valgus.”

The study, led by senior author Sunny Deo, FRCS(Orth), examined results with 812 Oxford Mobile Bearing Unicompartmental Knee Replacements (Biomet) implanted between September 2002 and September 2008. Twenty patients (21 knees) were identified who were revised to a total knee replacement (TKR) within 5 years of their index surgery.

Women comprised 81% of those requiring revision in the study, which focused on possible gender differences that might account for unicompartmenal knee replacement revision, according to Palmer.

“A number of studies have shown that aseptic loosening is the most common mode of failure, but in our data we found the most frequent cause of failure to be disease progression in the lateral compartment,” Palmer said.

AP X- ray shows UKR in an 81-year-old woman who experienced OA disease progression in the lateral compartment.

AP X-ray shows revision TKA in the same patient 53 months after the index UKR. Images: Palmer AJR

Based on radiological assessment of tibiofemoral valgus in the revision patients, the investigators determined valgus knee alignment was frequently increased, putting more load on the lateral compartment and resulting in lateral compartment OA disease progression, Palmer said.

Palmer and colleagues believe that overstuffing the implant is relatively easier in the female knee due to increased ligament and soft tissue envelope laxity.

“You should be mindful of overall alignment when making the first tibial cut and consider a smaller spacer to avoid pushing the knee too far into valgus,” he said.

In follow-up studies now underway, Palmer and colleagues are examining whether there are true gender differences in alignment and analyzing groups by how much their tibiofemoral angles changed to better understand that factor. – by Susan M. Rapp

Reference:

• Palmer AJR, et al. Revision of unicompartmental knee replacement (UKR) to total knee replacement (TKR): experience from a large district general hospital joint replacement unit. Presented at the 2010 Meeting of the Combined Orthopaedic Associations. Sept. 13-17, 2010. Glasgow.

• Antony J.R. Palmer, BMBCh, MA, MRCS, can be reached at Great Western Hospitals NHS Foundation Trust, Marlborough Road, Swindon SN3 6BB, UK; +44- 1793-6040020; e-mail: antony.palmer@gwh.nhs.uk.
• Disclosure: Palmer has no relevant financial disclosures.

The results reported in this paper are consistent with the results reported in the literature concerning mobile bearing UKR. In fact, historically, the first available UKRs were cemented fixed bearing all-polyethylene. In 1986, Goodfellow and O’Connor reported the first results of a mobile bearing metal-backed UKR designed to improve wear characteristics. Early retrieval studies confirmed this hypothesis. The results of the literature showed that precise alignment and ligament balancing is however essential to prevent mobile bearing dislocation or impingement and to avoid overcorrection, which may lead to rapid progression of arthritis in the opposite compartment. Earlier studies in the literature compared the re-intervention rate and the short- and mid-term survivorship after fixed or mobile bearing UKR. In the mobile bearing group, more early complications, potentially related to the patients’ indications, surgical technique and the fear of dislocation were observed, such as overcorrection of the deformation leading to early arthritis progression in the lateral compartment. These complications significantly impacted the survivorship of mobile bearing UKR. As underlined in this study, patient selection, identification of patient characteristics and surgical technique are key points to limit early complications observed after mobile bearing UKA.

— Sébastien Parratte, MD
Department of Orthopaedic Surgery
Sainte-Marguerite Hospital, Marseille
France

Disclosure: He has no relevant financial disclosures.

Reference:

• Goodfellow JW, et al. Clin Orthop Relat Res. 1986; 205:21-42.