Research Article: Time-dependent improvement in functional outcome following Oxford medial unicompartmental knee arthroplasty

Date Published: February 8, 2012

Publisher: Informa Healthcare

Author(s): Tor Kjetil Nerhus, Stig Heir, Ida Svege, Inge Skråmm, Tore Jervidalo, Jan Erik Madsen, Arne Ekeland.


10-year survival rates after unicompartmental knee replacement (UKR) have been up to 97% in single-center studies, but they have been as low as 80% in studies from arthroplasty registers. Few studies have evaluated short-term functional outcome and its improvement with time. We determined the time course of functional outcome as evaluated by the knee injury and osteoarthritis outcome score (KOOS) over the first 2 years after Oxford medial UKR.

In a prospective multicenter study, we included 99 unselected knees (96 patients, mean age 65 (51–80) years, 57 women) operated with Oxford medial UKR at 3 hospitals in the southeast of Norway between November 2003 and October 2006. Data were collected by independent investigators preoperatively and at 6 weeks, 3 months, 6 months, 1 year, and 2 years postoperatively. KOOS and range of motion (ROM) were determined at all follow-ups.

Mean KOOS values for pain and activities of daily living were improved already after 6 weeks, and increased between each time point up to 2 years postoperatively. However, no statistically significant improvements were seen after 6 months. Mean active and passive ROM gradually improved up to 2 years after UKR, and were then better than before surgery.

Most of the expected improvements in pain and function after UKR are achieved within 6 months of surgery. Only minimal improvement can be expected beyond this time.

Partial Text

96 unselected patients (99 knees) to be operated with medial unicompartmental knee arthroplasty at Martina Hansens Hospital, at Akershus University Hospital, and at Baerum Hospital between November 2003 and October 2006 were included in a prospective study. The inclusion criteria were: medial knee osteoarthritis, age 50–80 years, no rheumatoid arthritis or previous knee infection, a correctable varus deformity of less than 10°, a fixed flexion deformity of less than 10°, intact anterior and posterior cruciate ligaments, absence of osteoarthritis in the lateral compartment in standing radiographs, absence of lateral compartment tenderness, and no more than minimal patellofemoral symptoms or radiological abnormalities. Informed consent was obtained from all patients. All patients were operated with the Oxford phase III medial unicompartmental knee (Biomet Ltd., Bridgend, UK). The operation was performed in the hanging-leg position under spinal/epidural anesthesia, using a minimally invasive approach (Price et al. 2001). Mean operating time was 87 (52–152) min and 8 different surgeons were involved.

Data from all 96 patients (99 knees) initially included in the study were available for analysis.

To our knowledge, only 2 studies have used the KOOS to evaluate functional recovery after UKR (Lygre et al. 2010, Felts et al. 2010), and our study is the first to evaluate functional results after UKR using repetitive measures of the KOOS.