Hip Joint

There is no gold standard available in the Netherlands to determine the completeness of the LROI database. We therefore used 2 alternative methods. The data from the LROI were validated against reimbursement data from the national insurance database on healthcare (Vektis ). We also compared the data from the LROI with surgical date data from the HIS of each hospital. Completeness of registration in the LROI was calculated by comparing the number of registrations in the LROI with the number of arthroplasty surgeries based on national health insurance data (Vektis ), and with data from the HIS of each hospital in the Netherlands (for definitions, see box, for surgical codes see Table 2). Completeness based on Vektis data was calculated for the period 2009–2012, while completeness based on HIS data was calculated for 2012 and 2013.
A primary hip arthroplasty was defined as the first time a total, hemi-, or resurfacing prosthesis is placed, to replace a hip joint or part of a hip joint. A primary knee arthroplasty was defined as the first time a unicondylar, patellofemoral, or total prosthesis is placed, to replace a knee joint or part of a knee joint. Revision arthroplasty was defined as any change (replacement, removal, or addition) of 1 or several components of the joint prosthesis. As an aid to selecting the correct surgical procedures from the HIS, specific codes from the diagnosis treatment coding system used in Dutch healthcare were offered at hospitals.
Data from the LROI were retrieved in May 2014 and compared with data from Vektis for hip and knee arthroplasties performed at each hospital. In the analyses, counts were based on the total number of primary and revision arthroplasties (separately for hip and knee joints). Then, for the comparison with data from the HIS in each hospital in the Netherlands, primary and revision arthroplasties were analyzed separately for hip and knee joints. For primary hip arthroplasty, only total hip arthroplasties (THAs) were considered. In cases where the number of registrations per hospital in the LROI exceeded the amount of arthroplasty registrations in the Vektis or HIS data, the number in Vektis/HIS was considered the maximum number. Overall annual results and also hospital-specific results were calculated. Coverage of the LROI (participation of hospitals; see box for definition) was calculated by comparing the number of participating hospitals with the number of hospitals that performed arthroplasty procedures based on Vektis data for each year.

The participants performed maximal voluntary contraction (MVC) during isometric knee extension at knee joint angles of 90° and plantar flexion at ankle joint angles of 10° dorsiflexed position using a dynamometer mounting force transducer. The MVC measurements were performed on the right leg. First, we measured the knee extension and flexion MVC. The hip was fixed to the dynamometer using a strap with the hip joint at 90° flexion and the ankle was attached to a pad linked to a torque meter (VINE, Tokyo, Japan). The MVC trial included a gradual increase in knee extension force to maximum effort in 1 to 2 seconds, and a plateau phase at maximum effort was maintained for 4 seconds. Participants performed at least 2 trials with a ≥ 2-minute rest interval between them. The maximum MVC torque was selected for each trial. Subsequently, we measured the plantar flexion MVC. The hip was fixed to the dynamometer using a strap, with the hip joint at 90° flexion and the knee joint at full extension, and the ankle set on a pad linked to a torque meter (Takei Scientific Instruments, Niigata, Japan). The MVC trial was the same as that for knee extension. The maximum MVC torque was selected for each trial.